Thread Migration Preemption

RFC New Oleg Nesterov 3 participants 16 messages Jul 6, 2007 – Jul 14, 2007

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Oleg Nesterov

author

2007-07-06 06:03 UTC #0 lore raw

Quoted 21 lines · Mathieu Desnoyers

This patch adds the ability to protect critical sections from migration to another CPU without disabling preemption.
Typical use:
migration_disable();
local_inc(&__get_cpu_var(&my_local_t_var));
migration_enable();
kernel/sched.c +1 -0
@@ -1996,6 +1996,7 @@
 	 * 1) running (obviously), or
 	 * 2) cannot be migrated to this CPU due to cpus_allowed, or
 	 * 3) are cache-hot on their current CPU.
+	 * 4) migration preemption is non 0 for this non running task.
 	 */
 	if (!cpu_isset(this_cpu, p->cpus_allowed))
 		return 0;

kernel/sched.c line 2008

Quoted 5 lines

kernel/sched.c +2 -0

@@ -2003,6 +2004,8 @@
 
 	if (task_running(rq, p))
 		return 0;
+	if (task_thread_info(p)->migration_count)
+		return 0;

Question: This means that the task could be preempted, but can't sleep, yes?

Because try_to_wake_up() can change ->cpu. Shouldn't might_sleep() check ->migration_count then? Or we can change try_to_wake_up().

What if the task does copy_process() under migration_disable() ? Child gets a copy of ->migration_count.

Also, cpu_down() still can migrate this task to another CPU.

Oleg.

Mathieu Desnoyers

2007-07-06 14:23 UTC #1 lore raw

Quoted 23 lines · * Oleg Nesterov ([email protected]) wrote:

Quoted 22 lines · Mathieu Desnoyers
This patch adds the ability to protect critical sections from migration to another CPU without disabling preemption.
Typical use:
migration_disable();
local_inc(&__get_cpu_var(&my_local_t_var));
migration_enable();
kernel/sched.c +1 -0
@@ -1996,6 +1996,7 @@
 	 * 1) running (obviously), or
 	 * 2) cannot be migrated to this CPU due to cpus_allowed, or
 	 * 3) are cache-hot on their current CPU.
+	 * 4) migration preemption is non 0 for this non running task.
 	 */
 	if (!cpu_isset(this_cpu, p->cpus_allowed))
 		return 0;
@@ -2003,6 +2004,8 @@
 

Quoted 5 lines

kernel/sched.c line 2008

Quoted 4 lines

kernel/sched.c +2 -0

 	if (task_running(rq, p))
 		return 0;
+	if (task_thread_info(p)->migration_count)
+		return 0;

Hi Oleg,

Quoted 2 lines

Question: This means that the task could be preempted, but can't sleep, yes?

No exactly. This means that the task can be preempted, and can therefore sleep, but we do not allow this sleeping task to be migrated to a different CPU.

Quoted 3 lines

Because try_to_wake_up() can change ->cpu. Shouldn't might_sleep() check ->migration_count then? Or we can change try_to_wake_up().

If we look at try_to_wake_up, it seems to take the new_cpu from task_cpu(), which comes from the thread info ->cpu, updated by set_task_cpu(). The *_move_tasks seems to be responsible for calling can_migrate_task() to see if, in a deferred way, the migration_thread can use set_task_cpu() to change the task's cpu.

move_task_off_dead_cpu() does not seem to respect this though: it could potentially move away a process while it is in a critical section by forcing a __migrate_task. I guess I should put a test in __migrate_task also so move_task_off_dead_cpu() can try to repeat the migration.

Quoted 3 lines

What if the task does copy_process() under migration_disable() ? Child gets a copy of ->migration_count.

Right. Neighter does copy_process set the preemption count. It seems to be dealt by sched_fork() when the thread is first scheduled in to make sure that the preempt count is 1. I guess is would be safer to set the migration count to 0 there too. (or set it to one if we ever decide to make it the kernel default).

Quoted 2 lines

Also, cpu_down() still can migrate this task to another CPU.

Yes, just noted this earlier. I first thought it was using can_migrate_task(), but it does not seem so.

Thanks,

Mathieu

Quoted 2 lines

Oleg.

Signature · 3 lines

Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

Oleg Nesterov

author

2007-07-06 14:55 UTC #2 lore raw

Quoted 44 lines · Mathieu Desnoyers

Quoted 23 lines · * Oleg Nesterov ([email protected]) wrote:
Quoted 22 lines · Mathieu Desnoyers
This patch adds the ability to protect critical sections from migration to another CPU without disabling preemption.
Typical use:
migration_disable();
local_inc(&__get_cpu_var(&my_local_t_var));
migration_enable();
kernel/sched.c +1 -0
@@ -1996,6 +1996,7 @@
 	 * 1) running (obviously), or
 	 * 2) cannot be migrated to this CPU due to cpus_allowed, or
 	 * 3) are cache-hot on their current CPU.
+	 * 4) migration preemption is non 0 for this non running task.
 	 */
 	if (!cpu_isset(this_cpu, p->cpus_allowed))
 		return 0;
@@ -2003,6 +2004,8 @@
 
Quoted 5 lines
kernel/sched.c line 2008
Quoted 4 lines
kernel/sched.c +2 -0
 	if (task_running(rq, p))
 		return 0;
+	if (task_thread_info(p)->migration_count)
+		return 0;
Hi Oleg,
Quoted 2 lines
Question: This means that the task could be preempted, but can't sleep, yes?
No exactly. This means that the task can be preempted, and can therefore sleep, but we do not allow this sleeping task to be migrated to a different CPU.
Quoted 3 lines
Because try_to_wake_up() can change ->cpu. Shouldn't might_sleep() check ->migration_count then? Or we can change try_to_wake_up().

Quoted 5 lines

If we look at try_to_wake_up, it seems to take the new_cpu from task_cpu(), which comes from the thread info ->cpu, updated by set_task_cpu(). The *_move_tasks seems to be responsible for calling can_migrate_task() to see if, in a deferred way, the migration_thread can use set_task_cpu() to change the task's cpu.

Hmm. Perhaps I missed something, perhaps you... Or we both :)

try_to_wake_up() can choose new_cpu which differs from initial ->cpu. Then it does set_task_cpu() which just sets ->cpu, it doesn't check can_migrate_task(). This means that the task could be waken on another CPU, even if it sleeps under migration_disable().

Btw, I think you should also fix debug_smp_processor_id(), it won't like migration_disable() + __get_cpu_var().

Oleg.

Mathieu Desnoyers

2007-07-11 04:49 UTC #3 lore raw

Re: [RFC] Thread Migration Preemption - v2

Hi,

Still as an RFC, here is an updated version of the migration handling code in sched.c that supports migrate_disable()/migrate_enable().

I have taken care of the comments I received, thanks. I switched to migrate_enable/disable following Matt Mackall's comments. He also suggested to create, for now, an alias of migrate_disable/enable() to preempt_disable/enable() so that people could better identify what protection their code requires. This transition phase makes perfect sense to me.

A case study of scenarios where migration disabling without preemption disabling is useful must still be done, both for mainline kernel and for the -rt patch case. It basically involves any case where per-cpu data can be atomically updated using local atomic operations or where being tied to a CPU is important due to usage of its specific resources (performance counters could be a good example of this). We can also find, in the -rt kernel, the exemple of the threaded softirqs which must stay binded on a specific CPU and, due to performance reasons, cannot set the cpu affinity.

A new idea came to me recently: using migration disabling from user-space through a vsyscall page to protect accesses to per-cpu data in a locally atomic manner, which would be reentrant wrt signals and use less space than per thread data. I clearly see an interest for user-space tracing, where duplicating buffers per thread would be a waste of ressources. Since it is not possible to disable preemption from user-space context, disabling migration efficiently would be the solution that could provide critical regions bound to a CPU to user-space programs.

Mathieu

Thread Migration Preemption - v2

This patch adds the ability to protect critical sections from migration to another CPU without disabling preemption.

This will be useful to minimize the amount of preemption disabling for the -rt patch. It will help leveraging improvements brought by the local_t types in asm/local.h (see Documentation/local_ops.txt). Note that the updates done to variables protected by migrate_disable must be either atomic or protected from concurrent updates done by other threads.

Typical use:

migrate_disable();
local_inc(&__get_cpu_var(&my_local_t_var));
migrate_enable();

Which will increment the variable atomically wrt the local CPU.

Changes:

Do a check_migrate() upon migrate_enable() to answer to the migration thread waiting for us to exit the migration disabled critical section. Use a NEED_MIGRATE thread flag for this.

Note: (or we could say FIXME)
Is we ever want to check migration pending in assembly code, we will have to make sure we test the right thread flag bits on each architectures. Care should also be taken to check that the thread flags used won't trigger false positives in non selective asm thread flag checks.

Signed-off-by Mathieu Desnoyers <[email protected]>

---
 include/asm-alpha/thread_info.h     |    3 +
 include/asm-arm/thread_info.h       |    5 +
 include/asm-arm26/thread_info.h     |    5 +
 include/asm-avr32/thread_info.h     |    4 +
 include/asm-blackfin/thread_info.h  |    4 +
 include/asm-cris/thread_info.h      |    4 +
 include/asm-frv/thread_info.h       |    4 +
 include/asm-h8300/thread_info.h     |    4 +
 include/asm-i386/thread_info.h      |    6 +-
 include/asm-ia64/thread_info.h      |    4 +
 include/asm-m32r/thread_info.h      |    4 +
 include/asm-m68k/thread_info.h      |    2 
 include/asm-m68knommu/thread_info.h |    3 +
 include/asm-mips/thread_info.h      |    4 +
 include/asm-parisc/thread_info.h    |    4 +
 include/asm-powerpc/thread_info.h   |    4 +
 include/asm-s390/thread_info.h      |    4 +
 include/asm-sh/thread_info.h        |    4 +
 include/asm-sh64/thread_info.h      |    4 +
 include/asm-sparc/thread_info.h     |    4 +
 include/asm-sparc64/thread_info.h   |    5 +
 include/asm-um/thread_info.h        |    4 +
 include/asm-v850/thread_info.h      |    4 +
 include/asm-x86_64/thread_info.h    |    4 +
 include/asm-xtensa/thread_info.h    |    4 +
 include/linux/preempt.h             |   43 ++++++++++++++++
 kernel/sched.c                      |   92 +++++++++++++++++++++++++++++++++---
 lib/smp_processor_id.c              |    6 +-
 28 files changed, 230 insertions(+), 12 deletions(-)

include/asm-i386/thread_info.h +4 -2

Index: linux-2.6-lttng/include/asm-i386/thread_info.h
===================================================================
@@ -31,8 +31,7 @@
 	unsigned long		status;		/* thread-synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
-
-
+	int			migrate_count;/* 0: can migrate, <0: BUG */
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user-thead
 						   0-0xFFFFFFFF for kernel-thread

@@ -74,6 +73,7 @@
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\

@@ -132,6 +132,7 @@
 #define TIF_SYSCALL_AUDIT	6	/* syscall auditing active */
 #define TIF_SECCOMP		7	/* secure computing */
 #define TIF_RESTORE_SIGMASK	8	/* restore signal mask in do_signal() */
+#define TIF_NEED_MIGRATE	9	/* migration necessary */
 #define TIF_MEMDIE		16
 #define TIF_DEBUG		17	/* uses debug registers */
 #define TIF_IO_BITMAP		18	/* uses I/O bitmap */

@@ -147,6 +148,7 @@
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_DEBUG		(1<<TIF_DEBUG)
 #define _TIF_IO_BITMAP		(1<<TIF_IO_BITMAP)
 #define _TIF_FREEZE		(1<<TIF_FREEZE)

include/linux/preempt.h +42 -1

69 lines not on this page · raw message

kernel/sched.c +85 -7

171 lines not on this page · raw message

include/asm-alpha/thread_info.h +3 -0

Index: linux-2.6-lttng/include/asm-alpha/thread_info.h
===================================================================
@@ -21,6 +21,7 @@
 	mm_segment_t		addr_limit;	/* thread address space */
 	unsigned		cpu;		/* current CPU */
 	int			preempt_count; /* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	int bpt_nsaved;
 	unsigned long bpt_addr[2];		/* breakpoint handling  */

@@ -77,6 +78,7 @@
 #define TIF_MEMDIE		8
 #define TIF_RESTORE_SIGMASK	9	/* restore signal mask in do_signal */
 #define	TIF_SYSCALL_AUDIT	10
+#define TIF_NEED_MIGRATE	11	/* migration necessary */
 
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)

@@ -84,6 +86,7 @@
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 /* Work to do on interrupt/exception return.  */
 #define _TIF_WORK_MASK		(_TIF_SIGPENDING | _TIF_NEED_RESCHED)

include/asm-arm/thread_info.h +5 -0

Index: linux-2.6-lttng/include/asm-arm/thread_info.h
===================================================================
@@ -51,6 +51,7 @@
 struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	int			preempt_count;	/* 0 => preemptable, <0 => bug */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	mm_segment_t		addr_limit;	/* address limit */
 	struct task_struct	*task;		/* main task structure */
 	struct exec_domain	*exec_domain;	/* execution domain */

@@ -72,6 +73,7 @@
 	.exec_domain	= &default_exec_domain,				\
 	.flags		= 0,						\
 	.preempt_count	= 1,						\
+	.migrate_count = 0,						\
 	.addr_limit	= KERNEL_DS,					\
 	.cpu_domain	= domain_val(DOMAIN_USER, DOMAIN_MANAGER) |	\
 			  domain_val(DOMAIN_KERNEL, DOMAIN_MANAGER) |	\

@@ -137,12 +139,14 @@
  *  TIF_SYSCALL_TRACE	- syscall trace active
  *  TIF_SIGPENDING	- signal pending
  *  TIF_NEED_RESCHED	- rescheduling necessary
+ *  TIF_NEED_MIGRATE	- migration necessary
  *  TIF_USEDFPU		- FPU was used by this task this quantum (SMP)
  *  TIF_POLLING_NRFLAG	- true if poll_idle() is polling TIF_NEED_RESCHED
  *  TIF_SYSCALL_AUDIT	- Syscall audting active - LTTng
  */
 #define TIF_SIGPENDING		0
 #define TIF_NEED_RESCHED	1
+#define TIF_NEED_MIGRATE	2
 #define	TIF_SYSCALL_AUDIT	7
 #define TIF_SYSCALL_TRACE	8
 #define TIF_POLLING_NRFLAG	16

@@ -152,6 +156,7 @@
 
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define	_TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)

include/asm-arm26/thread_info.h +5 -0

Index: linux-2.6-lttng/include/asm-arm26/thread_info.h
===================================================================
@@ -45,6 +45,7 @@
 struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	int			preempt_count;	/* 0 => preemptable, <0 => bug */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	mm_segment_t		addr_limit;	/* address limit */
 	struct task_struct	*task;		/* main task structure */
 	struct exec_domain      *exec_domain;   /* execution domain */

@@ -60,6 +61,7 @@
 	.exec_domain	&default_exec_domain,	\
 	.flags		0,			\
 	.preempt_count	0,			\
+	.migrate_count 0,			\
 	.addr_limit	KERNEL_DS,		\
 	.restart_block  = {                             \
 		.fn     = do_no_restart_syscall,        \

@@ -112,11 +114,13 @@
  *  TIF_SYSCALL_TRACE	- syscall trace active
  *  TIF_SIGPENDING	- signal pending
  *  TIF_NEED_RESCHED	- rescheduling necessary
+ *  TIF_NEED_MIGRATE	- migration necessary
  *  TIF_USEDFPU		- FPU was used by this task this quantum (SMP)
  *  TIF_POLLING_NRFLAG	- true if poll_idle() is polling TIF_NEED_RESCHED
  */
 #define TIF_SIGPENDING		0
 #define TIF_NEED_RESCHED	1
+#define TIF_NEED_MIGRATE	2
 #define TIF_SYSCALL_TRACE	8
 #define TIF_USED_FPU		16
 #define TIF_POLLING_NRFLAG	17

@@ -124,6 +128,7 @@
 
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_USED_FPU		(1 << TIF_USED_FPU)
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)

include/asm-avr32/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-avr32/thread_info.h
===================================================================
@@ -25,6 +25,7 @@
 	unsigned long		flags;		/* low level flags */
 	__u32			cpu;
 	__s32			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	struct restart_block	restart_block;
 	__u8			supervisor_stack[0];
 };

@@ -36,6 +37,7 @@
 	.flags		= 0,						\
 	.cpu		= 0,						\
 	.preempt_count	= 1,						\
+	.migrate_count = 0,						\
 	.restart_block	= {						\
 		.fn	= do_no_restart_syscall				\
 	}								\

@@ -83,6 +85,7 @@
 #define TIF_MEMDIE		6
 #define TIF_RESTORE_SIGMASK	7	/* restore signal mask in do_signal */
 #define TIF_CPU_GOING_TO_SLEEP	8	/* CPU is entering sleep 0 mode */
+#define TIF_NEED_MIGRATE      9       /* migration necessary */
 #define TIF_USERSPACE		31      /* true if FS sets userspace */
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)

@@ -94,6 +97,7 @@
 #define _TIF_MEMDIE		(1 << TIF_MEMDIE)
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
 #define _TIF_CPU_GOING_TO_SLEEP (1 << TIF_CPU_GOING_TO_SLEEP)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 
 /* XXX: These two masks must never span more than 16 bits! */
 /* work to do on interrupt/exception return */

include/asm-blackfin/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-blackfin/thread_info.h
===================================================================
@@ -54,6 +54,7 @@
 	unsigned long flags;	/* low level flags */
 	int cpu;		/* cpu we're on */
 	int preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int migrate_count;	/* 0: can migrate, <0 => BUG */
 	mm_segment_t addr_limit;	/* address limit */
 	struct restart_block restart_block;
 	struct l1_scratch_task_info l1_task_info;

@@ -69,6 +70,7 @@
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count  = 1,                    \
+	.migrate_count = 0,			\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\
 	},					\

@@ -125,6 +127,7 @@
 #define TIF_MEMDIE              4
 #define TIF_RESTORE_SIGMASK	5	/* restore signal mask in do_signal() */
 #define TIF_FREEZE              6       /* is freezing for suspend */
+#define TIF_NEED_MIGRATE	7	/* migration necessary */
 
 /* as above, but as bit values */
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)

@@ -133,6 +136,7 @@
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 #define _TIF_FREEZE             (1<<TIF_FREEZE)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */

include/asm-cris/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-cris/thread_info.h
===================================================================
@@ -32,6 +32,7 @@
 	unsigned long		flags;		/* low level flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user-thead

@@ -58,6 +59,7 @@
 	.flags		= 0,				\
 	.cpu		= 0,				\
 	.preempt_count	= 1,				\
+	.migrate_count = 0,				\
 	.addr_limit	= KERNEL_DS,			\
 	.restart_block = {				\
 		       .fn = do_no_restart_syscall,	\

@@ -81,6 +83,7 @@
 #define TIF_SYSCALL_TRACE	0	/* syscall trace active */
 #define TIF_SIGPENDING		1	/* signal pending */
 #define TIF_NEED_RESCHED	2	/* rescheduling necessary */
+#define TIF_NEED_MIGRATE	3	/* migration necessary */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		17

@@ -88,6 +91,7 @@
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */
 #define _TIF_ALLWORK_MASK	0x0000FFFF	/* work to do on any return to u-space */

include/asm-frv/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-frv/thread_info.h
===================================================================
@@ -36,6 +36,7 @@
 	unsigned long		status;		/* thread-synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user-thead

@@ -68,6 +69,7 @@
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\

@@ -113,6 +115,7 @@
 #define TIF_SINGLESTEP		3	/* restore singlestep on return to user mode */
 #define TIF_IRET		4	/* return with iret */
 #define TIF_RESTORE_SIGMASK	5	/* restore signal mask in do_signal() */
+#define TIF_NEED_MIGRATE	6	/* migration necessary */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		17	/* OOM killer killed process */
 #define TIF_FREEZE		18	/* freezing for suspend */

@@ -125,6 +128,7 @@
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)
 #define _TIF_FREEZE		(1 << TIF_FREEZE)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */
 #define _TIF_ALLWORK_MASK	0x0000FFFF	/* work to do on any return to u-space */

include/asm-h8300/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-h8300/thread_info.h
===================================================================
@@ -24,6 +24,7 @@
 	unsigned long	   flags;		/* low level flags */
 	int		   cpu;			/* cpu we're on */
 	int		   preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	struct restart_block restart_block;
 };

@@ -37,6 +38,7 @@
 	.flags =	0,			\
 	.cpu =		0,			\
 	.preempt_count = 1,			\
+	.migrate_count = 0,			\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\
 	},					\

@@ -91,12 +93,14 @@
 #define TIF_POLLING_NRFLAG	3	/* true if poll_idle() is polling
 					   TIF_NEED_RESCHED */
 #define TIF_MEMDIE		4
+#define TIF_NEED_MIGRATE	5	/* migration necessary */
 
 /* as above, but as bit values */
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */

include/asm-ia64/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-ia64/thread_info.h
===================================================================
@@ -30,6 +30,7 @@
 	__u32 status;			/* Thread synchronous flags */
 	mm_segment_t addr_limit;	/* user-level address space limit */
 	int preempt_count;		/* 0=premptable, <0=BUG; will also serve as bh-counter */
+	int migrate_count;		/* 0: can migrate, <0 => BUG */
 	struct restart_block restart_block;
 };

@@ -43,6 +44,7 @@
 	.cpu		= 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.preempt_count	= 0,			\
+	.migrate_count = 0,			\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\
 	},					\

@@ -86,6 +88,7 @@
 #define TIF_SINGLESTEP		4	/* restore singlestep on return to user mode */
 #define TIF_RESTORE_SIGMASK	5	/* restore signal mask in do_signal() */
 #define TIF_PERFMON_WORK	6	/* work for pfm_handle_work() */
+#define TIF_NEED_MIGRATE	7	/* migration necessary */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		17
 #define TIF_MCA_INIT		18	/* this task is processing MCA or INIT */

@@ -98,6 +101,7 @@
 #define _TIF_SYSCALL_TRACEAUDIT	(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SINGLESTEP)
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
 #define _TIF_PERFMON_WORK	(1 << TIF_PERFMON_WORK)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)

include/asm-m32r/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-m32r/thread_info.h
===================================================================
@@ -29,6 +29,7 @@
 	unsigned long		status;		/* thread-synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user-thread

@@ -69,6 +70,7 @@
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\

@@ -150,6 +152,7 @@
 #define TIF_NEED_RESCHED	2	/* rescheduling necessary */
 #define TIF_SINGLESTEP		3	/* restore singlestep on return to user mode */
 #define TIF_IRET		4	/* return with iret */
+#define TIF_NEED_MIGRATE	5	/* migration necessary */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 					/* 31..28 fault code */
 #define TIF_MEMDIE		17

@@ -160,6 +163,7 @@
 #define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
 #define _TIF_IRET		(1<<TIF_IRET)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */
 #define _TIF_ALLWORK_MASK	0x0000FFFF	/* work to do on any return to u-space */

include/asm-m68k/thread_info.h +2 -0

Index: linux-2.6-lttng/include/asm-m68k/thread_info.h
===================================================================
@@ -9,6 +9,7 @@
 	unsigned long		flags;
 	struct exec_domain	*exec_domain;	/* execution domain */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	__u32 cpu; /* should always be 0 on m68k */
 	struct restart_block    restart_block;
 };

@@ -59,5 +60,6 @@
 #define TIF_DELAYED_TRACE	14	/* single step a syscall */
 #define TIF_SYSCALL_TRACE	15	/* syscall trace active */
 #define TIF_MEMDIE		16
+#define TIF_NEED_MIGRATE	17	/* migration necessary */
 
 #endif	/* _ASM_M68K_THREAD_INFO_H */

include/asm-m68knommu/thread_info.h +3 -0

Index: linux-2.6-lttng/include/asm-m68knommu/thread_info.h
===================================================================
@@ -37,6 +37,7 @@
 	unsigned long	   flags;		/* low level flags */
 	int		   cpu;			/* cpu we're on */
 	int		   preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int		   migrate_count;	/* 0: can migrate, <0 => BUG */
 	struct restart_block restart_block;
 };

@@ -88,6 +89,7 @@
 #define TIF_POLLING_NRFLAG	3	/* true if poll_idle() is polling
 					   TIF_NEED_RESCHED */
 #define TIF_MEMDIE		4
+#define TIF_NEED_MIGRATE	5	/* migration necessary */
 #define	TIF_SYSCALL_AUDIT	7	/* syscall auditing active */
 
 /* as above, but as bit values */

@@ -96,6 +98,7 @@
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_MEMDIE		(1<<TIF_MEMDIE)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */

include/asm-mips/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-mips/thread_info.h
===================================================================
@@ -28,6 +28,7 @@
 	unsigned long		tp_value;	/* thread pointer */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space:
 						   0-0xBFFFFFFF for user-thead

@@ -49,6 +50,7 @@
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\

@@ -113,6 +115,7 @@
 #define TIF_NEED_RESCHED	2	/* rescheduling necessary */
 #define TIF_SYSCALL_AUDIT	3	/* syscall auditing active */
 #define TIF_SECCOMP		4	/* secure computing */
+#define TIF_NEED_MIGRATE	5	/* migration necessary */
 #define TIF_RESTORE_SIGMASK	9	/* restore signal mask in do_signal() */
 #define TIF_USEDFPU		16	/* FPU was used by this task this quantum (SMP) */
 #define TIF_POLLING_NRFLAG	17	/* true if poll_idle() is polling TIF_NEED_RESCHED */

@@ -125,6 +128,7 @@
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 #define _TIF_USEDFPU		(1<<TIF_USEDFPU)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)

include/asm-parisc/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-parisc/thread_info.h
===================================================================
@@ -13,6 +13,7 @@
 	mm_segment_t addr_limit;	/* user-level address space limit */
 	__u32 cpu;			/* current CPU */
 	int preempt_count;		/* 0=premptable, <0=BUG; will also serve as bh-counter */
+	int migrate_count;		/* 0: can migrate, <0 => BUG */
 	struct restart_block restart_block;
 };

@@ -24,6 +25,7 @@
 	.cpu		= 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
   	.restart_block	= {			\
 		.fn = do_no_restart_syscall	\
 	}					\

@@ -62,6 +64,7 @@
 #define TIF_32BIT               4       /* 32 bit binary */
 #define TIF_MEMDIE		5
 #define TIF_RESTORE_SIGMASK	6	/* restore saved signal mask */
+#define TIF_NEED_MIGRATE	7	/* migration necessary */
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)

@@ -69,6 +72,7 @@
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)
 #define _TIF_32BIT		(1 << TIF_32BIT)
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 
 #define _TIF_USER_WORK_MASK     (_TIF_SIGPENDING | \
                                  _TIF_NEED_RESCHED | _TIF_RESTORE_SIGMASK)

include/asm-powerpc/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-powerpc/thread_info.h
===================================================================
@@ -35,6 +35,7 @@
 	int		cpu;			/* cpu we're on */
 	int		preempt_count;		/* 0 => preemptable,
 						   <0 => BUG */
+	int		migrate_count;	/* 0: can migrate, <0 => BUG */
 	struct restart_block restart_block;
 	unsigned long	local_flags;		/* private flags for thread */

@@ -53,6 +54,7 @@
 	.exec_domain =	&default_exec_domain,	\
 	.cpu =		0,			\
 	.preempt_count = 1,			\
+	.migrate_count = 0,			\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\
 	},					\

@@ -124,6 +126,7 @@
 #define TIF_FREEZE		14	/* Freezing for suspend */
 #define TIF_RUNLATCH		15	/* Is the runlatch enabled? */
 #define TIF_ABI_PENDING		16	/* 32/64 bit switch needed */
+#define TIF_NEED_MIGRATE	17	/* migration necessary */
 
 /* as above, but as bit values */
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)

@@ -142,6 +145,7 @@
 #define _TIF_FREEZE		(1<<TIF_FREEZE)
 #define _TIF_RUNLATCH		(1<<TIF_RUNLATCH)
 #define _TIF_ABI_PENDING	(1<<TIF_ABI_PENDING)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_SYSCALL_T_OR_A	(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SECCOMP)
 
 #define _TIF_USER_WORK_MASK	( _TIF_SIGPENDING | \

include/asm-s390/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-s390/thread_info.h
===================================================================
@@ -51,6 +51,7 @@
 	unsigned long		flags;		/* low level flags */
 	unsigned int		cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	struct restart_block	restart_block;
 };

@@ -64,6 +65,7 @@
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\
 	},					\

@@ -96,6 +98,7 @@
 #define TIF_SYSCALL_AUDIT	5	/* syscall auditing active */
 #define TIF_SINGLE_STEP		6	/* deliver sigtrap on return to user */
 #define TIF_MCCK_PENDING	7	/* machine check handling is pending */
+#define TIF_NEED_MIGRATE	8	/* migration necessary */
 #define TIF_USEDFPU		16	/* FPU was used by this task this quantum (SMP) */
 #define TIF_POLLING_NRFLAG	17	/* true if poll_idle() is polling 
 					   TIF_NEED_RESCHED */

@@ -110,6 +113,7 @@
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_SINGLE_STEP	(1<<TIF_SINGLE_STEP)
 #define _TIF_MCCK_PENDING	(1<<TIF_MCCK_PENDING)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_USEDFPU		(1<<TIF_USEDFPU)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_31BIT		(1<<TIF_31BIT)

include/asm-sh/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-sh/thread_info.h
===================================================================
@@ -21,6 +21,7 @@
 	unsigned long		flags;		/* low level flags */
 	__u32			cpu;
 	int			preempt_count; /* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	mm_segment_t		addr_limit;	/* thread address space */
 	struct restart_block	restart_block;
 	unsigned long		previous_sp;	/* sp of previous stack in case

@@ -58,6 +59,7 @@
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\

@@ -112,6 +114,7 @@
 #define TIF_RESTORE_SIGMASK	3	/* restore signal mask in do_signal() */
 #define TIF_SINGLESTEP		4	/* singlestepping active */
 #define	TIF_SYSCALL_AUDIT	6	/* syscall audit active */
+#define TIF_NEED_MIGRATE	7	/* migration necessary */
 #define TIF_USEDFPU		16	/* FPU was used by this task this quantum (SMP) */
 #define TIF_POLLING_NRFLAG	17	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		18

@@ -123,6 +126,7 @@
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 #define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_USEDFPU		(1<<TIF_USEDFPU)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_FREEZE		(1<<TIF_FREEZE)

include/asm-sh64/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-sh64/thread_info.h
===================================================================
@@ -23,6 +23,7 @@
 	unsigned long		flags;		/* low level flags */
 	/* Put the 4 32-bit fields together to make asm offsetting easier. */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	__u16			cpu;
 
 	mm_segment_t		addr_limit;

@@ -41,6 +42,7 @@
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit     = KERNEL_DS,            \
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\

@@ -80,12 +82,14 @@
 #define TIF_NEED_RESCHED	3	/* rescheduling necessary */
 #define TIF_MEMDIE		4
 #define TIF_RESTORE_SIGMASK	5	/* Restore signal mask in do_signal */
+#define TIF_NEED_MIGRATE	6	/* migration necessary */
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
 #define _TIF_MEMDIE		(1 << TIF_MEMDIE)
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 
 #endif /* __KERNEL__ */

include/asm-sparc/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-sparc/thread_info.h
===================================================================
@@ -33,6 +33,7 @@
 	int			cpu;		/* cpu we're on */
 	int			preempt_count;	/* 0 => preemptable,
 						   <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	int			softirq_count;
 	int			hardirq_count;

@@ -65,6 +66,7 @@
 	.flags		=	0,			\
 	.cpu		=	0,			\
 	.preempt_count	=	1,			\
+	.migrate_count =	0,			\
 	.restart_block	= {				\
 		.fn	=	do_no_restart_syscall,	\
 	},						\

@@ -132,6 +134,7 @@
 #define TIF_SIGPENDING		2	/* signal pending */
 #define TIF_NEED_RESCHED	3	/* rescheduling necessary */
 #define TIF_RESTORE_SIGMASK	4	/* restore signal mask in do_signal() */
+#define TIF_NEED_MIGRATE	5	/* migration necessary */
 #define TIF_USEDFPU		8	/* FPU was used by this task
 					 * this quantum (SMP) */
 #define TIF_POLLING_NRFLAG	9	/* true if poll_idle() is polling

@@ -144,6 +147,7 @@
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_USEDFPU		(1<<TIF_USEDFPU)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)

include/asm-sparc64/thread_info.h +4 -1

Index: linux-2.6-lttng/include/asm-sparc64/thread_info.h
===================================================================
@@ -47,6 +47,7 @@
 	struct pt_regs		*kregs;
 	struct exec_domain	*exec_domain;
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	__u8			new_child;
 	__u8			syscall_noerror;
 	__u16			cpu;

@@ -137,6 +138,7 @@
 	.flags		= ((unsigned long)ASI_P) << TI_FLAG_CURRENT_DS_SHIFT,	\
 	.exec_domain	=	&default_exec_domain,	\
 	.preempt_count	=	1,			\
+	.migrate_count =	0,			\
 	.restart_block	= {				\
 		.fn	=	do_no_restart_syscall,	\
 	},						\

@@ -225,7 +227,7 @@
 #define TIF_UNALIGNED		5	/* allowed to do unaligned accesses */
 #define TIF_NEWSIGNALS		6	/* wants new-style signals */
 #define TIF_32BIT		7	/* 32-bit binary */
-/* flag bit 8 is available */
+#define TIF_NEED_MIGRATE	8	/* migration necessary */
 #define TIF_SECCOMP		9	/* secure computing */
 #define TIF_SYSCALL_AUDIT	10	/* syscall auditing active */
 /* flag bit 11 is available */

@@ -244,6 +246,7 @@
 #define _TIF_UNALIGNED		(1<<TIF_UNALIGNED)
 #define _TIF_NEWSIGNALS		(1<<TIF_NEWSIGNALS)
 #define _TIF_32BIT		(1<<TIF_32BIT)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)

include/asm-um/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-um/thread_info.h
===================================================================
@@ -18,6 +18,7 @@
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;  /* 0 => preemptable,
 						   <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user
 						   0-0xFFFFFFFF for kernel */

@@ -32,6 +33,7 @@
 	.flags =		0,		\
 	.cpu =		0,			\
 	.preempt_count =	1,		\
+	.migrate_count =	0,		\
 	.addr_limit =	KERNEL_DS,		\
 	.restart_block =  {			\
 		.fn =  do_no_restart_syscall,	\

@@ -82,6 +84,7 @@
 #define TIF_MEMDIE	 	5
 #define TIF_SYSCALL_AUDIT	6
 #define TIF_RESTORE_SIGMASK	7
+#define TIF_NEED_MIGRATE	8	/* migration necessary */
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)

@@ -90,5 +93,6 @@
 #define _TIF_MEMDIE		(1 << TIF_MEMDIE)
 #define _TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 
 #endif

include/asm-v850/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-v850/thread_info.h
===================================================================
@@ -32,6 +32,7 @@
 	int			cpu;		/* cpu we're on */
 	int			preempt_count;	/* 0 => preemptable,
 						   <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	struct restart_block	restart_block;
 };

@@ -42,6 +43,7 @@
 	.flags =	0,						      \
 	.cpu =		0,						      \
 	.preempt_count = 1,						      \
+	.migrate_count = 0,						      \
 	.restart_block = {						      \
 		.fn = do_no_restart_syscall,				      \
 	},								      \

@@ -82,12 +84,14 @@
 #define TIF_POLLING_NRFLAG	3	/* true if poll_idle() is polling
 					   TIF_NEED_RESCHED */
 #define TIF_MEMDIE		4
+#define TIF_NEED_MIGRATE	5	/* migration necessary */
 
 /* as above, but as bit values */
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 
 /* Size of kernel stack for each process.  */

include/asm-x86_64/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-x86_64/thread_info.h
===================================================================
@@ -30,6 +30,7 @@
 	__u32			status;		/* thread synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int 			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	
 	struct restart_block    restart_block;

@@ -48,6 +49,7 @@
 	.flags	       = 0,			\
 	.cpu	       = 0,			\
 	.preempt_count = 1,			\
+	.migrate_count = 0,			\
 	.addr_limit     = KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\

@@ -115,6 +117,7 @@
 #define TIF_SECCOMP		8	/* secure computing */
 #define TIF_RESTORE_SIGMASK	9	/* restore signal mask in do_signal */
 #define TIF_MCE_NOTIFY		10	/* notify userspace of an MCE */
+#define TIF_NEED_MIGRATE	11	/* migration necessary */
 /* 16 free */
 #define TIF_IA32		17	/* 32bit process */ 
 #define TIF_FORK		18	/* ret_from_fork */

@@ -133,6 +136,7 @@
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 #define _TIF_MCE_NOTIFY		(1<<TIF_MCE_NOTIFY)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_IA32		(1<<TIF_IA32)
 #define _TIF_FORK		(1<<TIF_FORK)
 #define _TIF_ABI_PENDING	(1<<TIF_ABI_PENDING)

include/asm-xtensa/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-xtensa/thread_info.h
===================================================================
@@ -34,6 +34,7 @@
 	unsigned long		status;		/* thread-synchronous flags */
 	__u32			cpu;		/* current CPU */
 	__s32			preempt_count;	/* 0 => preemptable,< 0 => BUG*/
+	__s32			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space */
 	struct restart_block    restart_block;

@@ -72,6 +73,7 @@
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\

@@ -116,6 +118,7 @@
 #define TIF_IRET		4	/* return with iret */
 #define TIF_MEMDIE		5
 #define TIF_RESTORE_SIGMASK	6	/* restore signal mask in do_signal() */
+#define TIF_NEED_MIGRATE	7	/* migration necessary */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)

@@ -123,6 +126,7 @@
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
 #define _TIF_IRET		(1<<TIF_IRET)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)

lib/smp_processor_id.c +5 -1

Index: linux-2.6-lttng/lib/smp_processor_id.c
===================================================================
@@ -10,12 +10,16 @@
 unsigned int debug_smp_processor_id(void)
 {
 	unsigned long preempt_count = preempt_count();
+	unsigned long migrate_count = migrate_count();
 	int this_cpu = raw_smp_processor_id();
 	cpumask_t this_mask;
 
 	if (likely(preempt_count))
 		goto out;
 
+	if (likely(migrate_count))
+		goto out;
+
 	if (irqs_disabled())
 		goto out;

@@ -42,7 +46,7 @@
 	if (!printk_ratelimit())
 		goto out_enable;
 
-	printk(KERN_ERR "BUG: using smp_processor_id() in preemptible [%08x] code: %s/%d\n", preempt_count(), current->comm, current->pid);
+	printk(KERN_ERR "BUG: using smp_processor_id() in preemptible [%08x] migration [%08x] code: %s/%d\n", preempt_count(), migrate_count(), current->comm, current->pid);
 	print_symbol("caller is %s\n", (long)__builtin_return_address(0));
 	dump_stack();

Signature · 3 lines

Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

Oleg Nesterov

author

2007-07-11 16:35 UTC #4 lore raw

Re: [RFC] Thread Migration Preemption - v2

Quoted 10 lines · Mathieu Desnoyers

This patch adds the ability to protect critical sections from migration to another CPU without disabling preemption.
This will be useful to minimize the amount of preemption disabling for the -rt patch. It will help leveraging improvements brought by the local_t types in asm/local.h (see Documentation/local_ops.txt). Note that the updates done to variables protected by migrate_disable must be either atomic or protected from concurrent updates done by other threads.

Quoted 7 lines

Typical use:
migrate_disable();
local_inc(&__get_cpu_var(&my_local_t_var));
migrate_enable();
Which will increment the variable atomically wrt the local CPU.

Well, I am not a maintainer, but I personally think this patch is too complex.

Mathieu, please use "diff -p", it is very difficult to read it. I am not sure I understand this patch correctly, I don't have a -git tree.

kernel/sched.c line 4894

Quoted 11 lines

static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu) {

kernel/sched.c +3 -1

@@ -4829,13 +4888,19 @@
 
 	double_rq_lock(rq_src, rq_dest);
 	/* Already moved. */
-	if (task_cpu(p) != src_cpu)
+	if (task_cpu(p) != src_cpu) {
+		ret = 1;
 		goto out;
+	}

This is a strange change. Why we return success when migration failed ? OK, I guess this is a special hack for the modified migration_thread()...

kernel/sched.c line 4903

Quoted 9 lines

kernel/sched.c +4 -0

 	/* Affinity changed (again). */
 	if (!cpu_isset(dest_cpu, p->cpus_allowed))
 		goto out;
 
 	on_rq = p->se.on_rq;
+#ifdef CONFIG_PREEMPT
+	if (!on_rq && task_thread_info(p)->migrate_count)
+		goto out;
+#endif

This means that move_task_off_dead_cpu() will spin until the task will be scheduled on the dead CPU. Given that we hold tasklist_lock and irqs are disabled, this may never happen.

(This patch adds a lot of #ifdef's, I think it could be simplified if you add
get_migrate_count() which is defined as 0 when !CONFIG_PREEMPT).

Quoted 13 lines

kernel/sched.c +5 -3

@@ -4891,10 +4957,22 @@
 		list_del_init(head->next);
 
 		spin_unlock(&rq->lock);
-		__migrate_task(req->task, cpu, req->dest_cpu);
+		migrated = __migrate_task(req->task, cpu, req->dest_cpu);
 		local_irq_enable();
-
-		complete(&req->done);
+		if (!migrated) {
+			/*
+			 * If the process has not been migrated, let it run
+			 * until it reaches a migration_check() so it can

kernel/sched.c line 4975

Quoted 10 lines

kernel/sched.c +10 -0

+			 * wake us up.
+			 */
+			spin_lock_irq(&rq->lock);
+			head = &rq->migration_queue;
+			list_add(&req->list, head);
+			set_tsk_thread_flag(req->task, TIF_NEED_MIGRATE);
+			spin_unlock_irq(&rq->lock);
+			wake_up_process(req->task);
+		} else
+			complete(&req->done);

I guess this is migration_thread(). The wake_up_process(req->task) looks strange, why? It can't help if the task waits for the event/mutex.

And this is racy. What if check_migrate() is in progress, and the task has already checked TIF_NEED_MIGRATE?

Hm. We re-add "req" to rq->migration_queue. This means that migration_thread() will do a busy-wait loop. Not good and deadlockable, migration/X is SCHED_FIFO. And what if __migrate_task() failed because ->cpus_allowed was changed in between?

Oleg.

Mathieu Desnoyers

2007-07-14 18:27 UTC #5 lore raw

Re: [RFC] Thread Migration Preemption - v2

Quoted 17 lines · * Oleg Nesterov ([email protected]) wrote:

Quoted 16 lines · Mathieu Desnoyers
This patch adds the ability to protect critical sections from migration to another CPU without disabling preemption.
This will be useful to minimize the amount of preemption disabling for the -rt patch. It will help leveraging improvements brought by the local_t types in asm/local.h (see Documentation/local_ops.txt). Note that the updates done to variables protected by migrate_disable must be either atomic or protected from concurrent updates done by other threads.
Typical use:
migrate_disable();
local_inc(&__get_cpu_var(&my_local_t_var));
migrate_enable();

Quoted 7 lines

Quoted 1 line
Which will increment the variable atomically wrt the local CPU.
Well, I am not a maintainer, but I personally think this patch is too complex.
Mathieu, please use "diff -p", it is very difficult to read it. I am not sure I understand this patch correctly, I don't have a -git tree.

man quilt... echo "QUILT_DIFF_OPTS="-p" > ~/.quiltrc. done. :) Thanks for pointing this out, the next patches should include this.

Quoted 4 lines

Quoted 4 lines
static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu) {
(quoted diff) +0 -0
@@ -4829,13 +4888,19 @@
 

Quoted 11 lines

kernel/sched.c line 4894
Quoted 7 lines
kernel/sched.c +3 -1
 	double_rq_lock(rq_src, rq_dest);
 	/* Already moved. */
-	if (task_cpu(p) != src_cpu)
+	if (task_cpu(p) != src_cpu) {
+		ret = 1;
 		goto out;
+	}
This is a strange change. Why we return success when migration failed ? OK, I guess this is a special hack for the modified migration_thread()...

Yes, I wanted to change __migrate_task so it returns true if, after it has been called to migrate a task out of a source CPU, the task is indeed now migrated out the this CPU.

It follows a comment already at the beginning of this function:

* So we race with normal scheduler movements, but that's OK, as long
* as the task is no longer on this CPU.

The comment at the beginning explains the new convention:

- * Returns non-zero if task was successfully migrated.
+ * Returns non-zero if task is on dest_cpu when this function ends.

Well.. my comment is not perfect. It should read:

- * Returns non-zero if task was successfully migrated.
+ * Returns non-zero if task is not on src_cpu when this function ends.

My assumption is that if migrate_task races with the scheduler movement to move a task out of a CPU, it should return non-zero in every case when the task has been migrated out of the src_cpu.

Quoted 4 lines

kernel/sched.c +0 -0

 	/* Affinity changed (again). */
 	if (!cpu_isset(dest_cpu, p->cpus_allowed))
 		goto out;

Quoted 10 lines

kernel/sched.c line 4903
Quoted 5 lines
kernel/sched.c +4 -0
 	on_rq = p->se.on_rq;
+#ifdef CONFIG_PREEMPT
+	if (!on_rq && task_thread_info(p)->migrate_count)
+		goto out;
+#endif
This means that move_task_off_dead_cpu() will spin until the task will be scheduled on the dead CPU. Given that we hold tasklist_lock and irqs are disabled, this may never happen.

Yes. My idea to fix this issue is the following:

If a thread has non zero migrate_count, we should still move it to a different CPU upon hotplug cpu removal, even if this thread resists migration. Care should be taken to send _all_ such threads to the _same_ CPU so they don't race for the per-cpu ressources. Does it make sense ?

We would have to keep the CPU affinity of the threads running on the wrong CPU until they end their migrate disabled section, so that we can put them back on their original CPU if it goes back online, otherwise we could end up with concurrent per-cpu variables accesses.

(I'll wait for reply before coding a solution for this CPU HOTPLUG related problem)

Quoted 2 lines

(This patch adds a lot of #ifdef's, I think it could be simplified if you add
get_migrate_count() which is defined as 0 when !CONFIG_PREEMPT).

Sure. Added migrate_count() and task_migrate_count(task).

Quoted 19 lines

kernel/sched.c +10 -3

@@ -4891,10 +4957,22 @@
 		list_del_init(head->next);
 
 		spin_unlock(&rq->lock);
-		__migrate_task(req->task, cpu, req->dest_cpu);
+		migrated = __migrate_task(req->task, cpu, req->dest_cpu);
 		local_irq_enable();
-
-		complete(&req->done);
+		if (!migrated) {
+			/*
+			 * If the process has not been migrated, let it run
+			 * until it reaches a migration_check() so it can
+			 * wake us up.
+			 */
+			spin_lock_irq(&rq->lock);
+			head = &rq->migration_queue;
+			list_add(&req->list, head);

Quoted 9 lines

kernel/sched.c line 4975
Quoted 5 lines
kernel/sched.c +5 -0
+			set_tsk_thread_flag(req->task, TIF_NEED_MIGRATE);
+			spin_unlock_irq(&rq->lock);
+			wake_up_process(req->task);
+		} else
+			complete(&req->done);
I guess this is migration_thread(). The wake_up_process(req->task) looks strange, why? It can't help if the task waits for the event/mutex.

Hrm, the idea was to wake up the thread that is in the migrate disabled section, which is what I seem to do req->task points to the process we try to migrate. We poke it like this until is ends its critical section. At that moment, the thread will wake up the migration thread, and only then do we let sched_migrate_task, which is waiting for completion, finish.

Quoted 3 lines

And this is racy. What if check_migrate() is in progress, and the task has already checked TIF_NEED_MIGRATE?

The idea is to take the rq->lock to make sure the thread is not running when we do this. Since the runqueue lock is released between the tests in __migrate_task and this code, I should test again to see if it is running. Currently, the migration thread retries actively if the thread we are trying to migrate is in its critical section. The change I am about to do does 2 things:

If the thread is on the runqueue, retry actively.
If the thread is not on the runqueue, set the NEED MIGRATE flag and go to sleep, waiting for it to wake us up.

Quoted 2 lines

Hm. We re-add "req" to rq->migration_queue. This means that migration_thread() will do a busy-wait loop. Not good and deadlockable, migration/X is SCHED_FIFO.

Yup. The comment above should hopefully fix it.

Quoted 2 lines

And what if __migrate_task() failed because ->cpus_allowed was changed in between?

Right, we should check for this. Will fix.

Thanks for the thorough review.

Mathieu

Quoted 2 lines

Oleg.

Signature · 3 lines

Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

Oleg Nesterov

author

2007-07-14 19:56 UTC #6 lore raw

Re: [RFC] Thread Migration Preemption - v2

Quoted 24 lines · Mathieu Desnoyers

Quoted 4 lines · * Oleg Nesterov ([email protected]) wrote:
Quoted 4 lines
kernel/sched.c +0 -0
 	/* Affinity changed (again). */
 	if (!cpu_isset(dest_cpu, p->cpus_allowed))
 		goto out;
Quoted 10 lines
kernel/sched.c line 4903
Quoted 5 lines
kernel/sched.c +4 -0
 	on_rq = p->se.on_rq;
+#ifdef CONFIG_PREEMPT
+	if (!on_rq && task_thread_info(p)->migrate_count)
+		goto out;
+#endif
This means that move_task_off_dead_cpu() will spin until the task will be scheduled on the dead CPU. Given that we hold tasklist_lock and irqs are disabled, this may never happen.
Yes. My idea to fix this issue is the following:
If a thread has non zero migrate_count, we should still move it to a different CPU upon hotplug cpu removal, even if this thread resists migration. Care should be taken to send _all_ such threads to the _same_ CPU so they don't race for the per-cpu ressources. Does it make sense ?

Quoted 4 lines

We would have to keep the CPU affinity of the threads running on the wrong CPU until they end their migrate disabled section, so that we can put them back on their original CPU if it goes back online, otherwise we could end up with concurrent per-cpu variables accesses.

Well, this means that migrate_disable() doesn't guarantee a stable smp_processor_id(), not good.

Quoted 28 lines

Quoted 18 lines

kernel/sched.c +10 -3

@@ -4891,10 +4957,22 @@
 		list_del_init(head->next);
 
 		spin_unlock(&rq->lock);
-		__migrate_task(req->task, cpu, req->dest_cpu);
+		migrated = __migrate_task(req->task, cpu, req->dest_cpu);
 		local_irq_enable();
-
-		complete(&req->done);
+		if (!migrated) {
+			/*
+			 * If the process has not been migrated, let it run
+			 * until it reaches a migration_check() so it can
+			 * wake us up.
+			 */
+			spin_lock_irq(&rq->lock);
+			head = &rq->migration_queue;
+			list_add(&req->list, head);

Quoted 9 lines

kernel/sched.c line 4975
Quoted 5 lines
kernel/sched.c +5 -0
+			set_tsk_thread_flag(req->task, TIF_NEED_MIGRATE);
+			spin_unlock_irq(&rq->lock);
+			wake_up_process(req->task);
+		} else
+			complete(&req->done);
I guess this is migration_thread(). The wake_up_process(req->task) looks strange, why? It can't help if the task waits for the event/mutex.

Quoted 4 lines

Hrm, the idea was to wake up the thread that is in the migrate disabled section, which is what I seem to do req->task points to the process we try to migrate. We poke it like this until is ends its critical section.

But this can only waste CPU, nothing more, no? Suppose that req->thread sleeps waiting for the mutex. You can wake it up, and it will call schedule() again.

This can help if req->thread does something like schedule_timeout(), but I don't think this is a common case.

Oleg.

Mathieu Desnoyers

2007-07-14 18:40 UTC #7 lore raw

RFC 1/1 Thread Migration Preemption - v3

In reply to Oleg Nesterov

Thread Migration Preemption

This patch adds the ability to protect critical sections from migration to another CPU without disabling preemption.

Typical use:

migrate_disable();
local_inc(&__get_cpu_var(&my_local_t_var));
migrate_enable();

Which will increment the variable atomically wrt the local CPU.

Changes:

Do a check_migrate() upon migrate_enable() to answer to the migration thread waiting for us to exit the migration disabled critical section. Use a NEED_MIGRATE thread flag for this.

FIXME (HOTPLUG) :

Quoted 4 lines

    /* Affinity changed (again). */
    if (!cpu_isset(dest_cpu, p->cpus_allowed))
            goto out;

Quoted 12 lines

Review
Quoted 5 lines
    on_rq = p->se.on_rq;
(quoted diff) +4 -0
+#ifdef CONFIG_PREEMPT
+   if (!on_rq && task_thread_info(p)->migrate_count)
+           goto out;
+#endif
This means that move_task_off_dead_cpu() will spin until the task will be scheduled
on the dead CPU. Given that we hold tasklist_lock and irqs are disabled, this may
never happen.

Yes. My idea to fix this issue is the following:

(I'll wait for reply before coding a solution for this CPU HOTPLUG related problem)

Signed-off-by Mathieu Desnoyers <[email protected]>

---
 include/asm-alpha/thread_info.h     |    3 +
 include/asm-arm/thread_info.h       |    5 +
 include/asm-arm26/thread_info.h     |    5 +
 include/asm-avr32/thread_info.h     |    4 +
 include/asm-blackfin/thread_info.h  |    4 +
 include/asm-cris/thread_info.h      |    4 +
 include/asm-frv/thread_info.h       |    4 +
 include/asm-h8300/thread_info.h     |    4 +
 include/asm-i386/thread_info.h      |    6 +-
 include/asm-ia64/thread_info.h      |    4 +
 include/asm-m32r/thread_info.h      |    4 +
 include/asm-m68k/thread_info.h      |    2 
 include/asm-m68knommu/thread_info.h |    3 +
 include/asm-mips/thread_info.h      |    4 +
 include/asm-parisc/thread_info.h    |    4 +
 include/asm-powerpc/thread_info.h   |    4 +
 include/asm-s390/thread_info.h      |    4 +
 include/asm-sh/thread_info.h        |    4 +
 include/asm-sh64/thread_info.h      |    4 +
 include/asm-sparc/thread_info.h     |    4 +
 include/asm-sparc64/thread_info.h   |    5 +
 include/asm-um/thread_info.h        |    4 +
 include/asm-v850/thread_info.h      |    4 +
 include/asm-x86_64/thread_info.h    |    4 +
 include/asm-xtensa/thread_info.h    |    4 +
 include/linux/preempt.h             |   47 ++++++++++++++++-
 kernel/sched.c                      |   98 +++++++++++++++++++++++++++++++++---
 lib/smp_processor_id.c              |    6 +-
 28 files changed, 240 insertions(+), 12 deletions(-)

include/asm-i386/thread_info.h +4 -2

Index: linux-2.6-lttng/include/asm-i386/thread_info.h
===================================================================
@@ -31,8 +31,7 @@ struct thread_info {
 	unsigned long		status;		/* thread-synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
-
-
+	int			migrate_count;/* 0: can migrate, <0: BUG */
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user-thead
 						   0-0xFFFFFFFF for kernel-thread

@@ -74,6 +73,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\

@@ -132,6 +132,7 @@ static inline struct thread_info *curren
 #define TIF_SYSCALL_AUDIT	6	/* syscall auditing active */
 #define TIF_SECCOMP		7	/* secure computing */
 #define TIF_RESTORE_SIGMASK	8	/* restore signal mask in do_signal() */
+#define TIF_NEED_MIGRATE	9	/* migration necessary */
 #define TIF_MEMDIE		16
 #define TIF_DEBUG		17	/* uses debug registers */
 #define TIF_IO_BITMAP		18	/* uses I/O bitmap */

@@ -147,6 +148,7 @@ static inline struct thread_info *curren
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_DEBUG		(1<<TIF_DEBUG)
 #define _TIF_IO_BITMAP		(1<<TIF_IO_BITMAP)
 #define _TIF_FREEZE		(1<<TIF_FREEZE)

include/linux/preempt.h +46 -1

73 lines not on this page · raw message

kernel/sched.c +91 -7

177 lines not on this page · raw message

include/asm-alpha/thread_info.h +3 -0

Index: linux-2.6-lttng/include/asm-alpha/thread_info.h
===================================================================
@@ -21,6 +21,7 @@ struct thread_info {
 	mm_segment_t		addr_limit;	/* thread address space */
 	unsigned		cpu;		/* current CPU */
 	int			preempt_count; /* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	int bpt_nsaved;
 	unsigned long bpt_addr[2];		/* breakpoint handling  */

@@ -77,6 +78,7 @@ register struct thread_info *__current_t
 #define TIF_MEMDIE		8
 #define TIF_RESTORE_SIGMASK	9	/* restore signal mask in do_signal */
 #define	TIF_SYSCALL_AUDIT	10
+#define TIF_NEED_MIGRATE	11	/* migration necessary */
 
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)

@@ -84,6 +86,7 @@ register struct thread_info *__current_t
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 /* Work to do on interrupt/exception return.  */
 #define _TIF_WORK_MASK		(_TIF_SIGPENDING | _TIF_NEED_RESCHED)

include/asm-arm/thread_info.h +5 -0

Index: linux-2.6-lttng/include/asm-arm/thread_info.h
===================================================================
@@ -51,6 +51,7 @@ struct cpu_context_save {
 struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	int			preempt_count;	/* 0 => preemptable, <0 => bug */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	mm_segment_t		addr_limit;	/* address limit */
 	struct task_struct	*task;		/* main task structure */
 	struct exec_domain	*exec_domain;	/* execution domain */

@@ -72,6 +73,7 @@ struct thread_info {
 	.exec_domain	= &default_exec_domain,				\
 	.flags		= 0,						\
 	.preempt_count	= 1,						\
+	.migrate_count = 0,						\
 	.addr_limit	= KERNEL_DS,					\
 	.cpu_domain	= domain_val(DOMAIN_USER, DOMAIN_MANAGER) |	\
 			  domain_val(DOMAIN_KERNEL, DOMAIN_MANAGER) |	\

@@ -137,12 +139,14 @@ extern void iwmmxt_task_switch(struct th
  *  TIF_SYSCALL_TRACE	- syscall trace active
  *  TIF_SIGPENDING	- signal pending
  *  TIF_NEED_RESCHED	- rescheduling necessary
+ *  TIF_NEED_MIGRATE	- migration necessary
  *  TIF_USEDFPU		- FPU was used by this task this quantum (SMP)
  *  TIF_POLLING_NRFLAG	- true if poll_idle() is polling TIF_NEED_RESCHED
  *  TIF_SYSCALL_AUDIT	- Syscall audting active - LTTng
  */
 #define TIF_SIGPENDING		0
 #define TIF_NEED_RESCHED	1
+#define TIF_NEED_MIGRATE	2
 #define	TIF_SYSCALL_AUDIT	7
 #define TIF_SYSCALL_TRACE	8
 #define TIF_POLLING_NRFLAG	16

@@ -152,6 +156,7 @@ extern void iwmmxt_task_switch(struct th
 
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define	_TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)

include/asm-arm26/thread_info.h +5 -0

Index: linux-2.6-lttng/include/asm-arm26/thread_info.h
===================================================================
@@ -45,6 +45,7 @@ struct cpu_context_save {
 struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	int			preempt_count;	/* 0 => preemptable, <0 => bug */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	mm_segment_t		addr_limit;	/* address limit */
 	struct task_struct	*task;		/* main task structure */
 	struct exec_domain      *exec_domain;   /* execution domain */

@@ -60,6 +61,7 @@ struct thread_info {
 	.exec_domain	&default_exec_domain,	\
 	.flags		0,			\
 	.preempt_count	0,			\
+	.migrate_count 0,			\
 	.addr_limit	KERNEL_DS,		\
 	.restart_block  = {                             \
 		.fn     = do_no_restart_syscall,        \

@@ -112,11 +114,13 @@ extern void free_thread_info(struct thre
  *  TIF_SYSCALL_TRACE	- syscall trace active
  *  TIF_SIGPENDING	- signal pending
  *  TIF_NEED_RESCHED	- rescheduling necessary
+ *  TIF_NEED_MIGRATE	- migration necessary
  *  TIF_USEDFPU		- FPU was used by this task this quantum (SMP)
  *  TIF_POLLING_NRFLAG	- true if poll_idle() is polling TIF_NEED_RESCHED
  */
 #define TIF_SIGPENDING		0
 #define TIF_NEED_RESCHED	1
+#define TIF_NEED_MIGRATE	2
 #define TIF_SYSCALL_TRACE	8
 #define TIF_USED_FPU		16
 #define TIF_POLLING_NRFLAG	17

@@ -124,6 +128,7 @@ extern void free_thread_info(struct thre
 
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_USED_FPU		(1 << TIF_USED_FPU)
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)

include/asm-avr32/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-avr32/thread_info.h
===================================================================
@@ -25,6 +25,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	__u32			cpu;
 	__s32			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	struct restart_block	restart_block;
 	__u8			supervisor_stack[0];
 };

@@ -36,6 +37,7 @@ struct thread_info {
 	.flags		= 0,						\
 	.cpu		= 0,						\
 	.preempt_count	= 1,						\
+	.migrate_count = 0,						\
 	.restart_block	= {						\
 		.fn	= do_no_restart_syscall				\
 	}								\

@@ -83,6 +85,7 @@ static inline struct thread_info *curren
 #define TIF_MEMDIE		6
 #define TIF_RESTORE_SIGMASK	7	/* restore signal mask in do_signal */
 #define TIF_CPU_GOING_TO_SLEEP	8	/* CPU is entering sleep 0 mode */
+#define TIF_NEED_MIGRATE      9       /* migration necessary */
 #define TIF_USERSPACE		31      /* true if FS sets userspace */
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)

@@ -94,6 +97,7 @@ static inline struct thread_info *curren
 #define _TIF_MEMDIE		(1 << TIF_MEMDIE)
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
 #define _TIF_CPU_GOING_TO_SLEEP (1 << TIF_CPU_GOING_TO_SLEEP)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 
 /* XXX: These two masks must never span more than 16 bits! */
 /* work to do on interrupt/exception return */

include/asm-blackfin/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-blackfin/thread_info.h
===================================================================
@@ -54,6 +54,7 @@ struct thread_info {
 	unsigned long flags;	/* low level flags */
 	int cpu;		/* cpu we're on */
 	int preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int migrate_count;	/* 0: can migrate, <0 => BUG */
 	mm_segment_t addr_limit;	/* address limit */
 	struct restart_block restart_block;
 	struct l1_scratch_task_info l1_task_info;

@@ -69,6 +70,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count  = 1,                    \
+	.migrate_count = 0,			\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\
 	},					\

@@ -125,6 +127,7 @@ static inline struct thread_info *curren
 #define TIF_MEMDIE              4
 #define TIF_RESTORE_SIGMASK	5	/* restore signal mask in do_signal() */
 #define TIF_FREEZE              6       /* is freezing for suspend */
+#define TIF_NEED_MIGRATE	7	/* migration necessary */
 
 /* as above, but as bit values */
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)

@@ -133,6 +136,7 @@ static inline struct thread_info *curren
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 #define _TIF_FREEZE             (1<<TIF_FREEZE)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */

include/asm-cris/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-cris/thread_info.h
===================================================================
@@ -32,6 +32,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user-thead

@@ -58,6 +59,7 @@ struct thread_info {
 	.flags		= 0,				\
 	.cpu		= 0,				\
 	.preempt_count	= 1,				\
+	.migrate_count = 0,				\
 	.addr_limit	= KERNEL_DS,			\
 	.restart_block = {				\
 		       .fn = do_no_restart_syscall,	\

@@ -81,6 +83,7 @@ struct thread_info {
 #define TIF_SYSCALL_TRACE	0	/* syscall trace active */
 #define TIF_SIGPENDING		1	/* signal pending */
 #define TIF_NEED_RESCHED	2	/* rescheduling necessary */
+#define TIF_NEED_MIGRATE	3	/* migration necessary */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		17

@@ -88,6 +91,7 @@ struct thread_info {
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */
 #define _TIF_ALLWORK_MASK	0x0000FFFF	/* work to do on any return to u-space */

include/asm-frv/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-frv/thread_info.h
===================================================================
@@ -36,6 +36,7 @@ struct thread_info {
 	unsigned long		status;		/* thread-synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user-thead

@@ -68,6 +69,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\

@@ -113,6 +115,7 @@ register struct thread_info *__current_t
 #define TIF_SINGLESTEP		3	/* restore singlestep on return to user mode */
 #define TIF_IRET		4	/* return with iret */
 #define TIF_RESTORE_SIGMASK	5	/* restore signal mask in do_signal() */
+#define TIF_NEED_MIGRATE	6	/* migration necessary */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		17	/* OOM killer killed process */
 #define TIF_FREEZE		18	/* freezing for suspend */

@@ -125,6 +128,7 @@ register struct thread_info *__current_t
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)
 #define _TIF_FREEZE		(1 << TIF_FREEZE)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */
 #define _TIF_ALLWORK_MASK	0x0000FFFF	/* work to do on any return to u-space */

include/asm-h8300/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-h8300/thread_info.h
===================================================================
@@ -24,6 +24,7 @@ struct thread_info {
 	unsigned long	   flags;		/* low level flags */
 	int		   cpu;			/* cpu we're on */
 	int		   preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	struct restart_block restart_block;
 };

@@ -37,6 +38,7 @@ struct thread_info {
 	.flags =	0,			\
 	.cpu =		0,			\
 	.preempt_count = 1,			\
+	.migrate_count = 0,			\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\
 	},					\

@@ -91,12 +93,14 @@ static inline struct thread_info *curren
 #define TIF_POLLING_NRFLAG	3	/* true if poll_idle() is polling
 					   TIF_NEED_RESCHED */
 #define TIF_MEMDIE		4
+#define TIF_NEED_MIGRATE	5	/* migration necessary */
 
 /* as above, but as bit values */
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */

include/asm-ia64/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-ia64/thread_info.h
===================================================================
@@ -30,6 +30,7 @@ struct thread_info {
 	__u32 status;			/* Thread synchronous flags */
 	mm_segment_t addr_limit;	/* user-level address space limit */
 	int preempt_count;		/* 0=premptable, <0=BUG; will also serve as bh-counter */
+	int migrate_count;		/* 0: can migrate, <0 => BUG */
 	struct restart_block restart_block;
 };

@@ -43,6 +44,7 @@ struct thread_info {
 	.cpu		= 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.preempt_count	= 0,			\
+	.migrate_count = 0,			\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\
 	},					\

@@ -86,6 +88,7 @@ struct thread_info {
 #define TIF_SINGLESTEP		4	/* restore singlestep on return to user mode */
 #define TIF_RESTORE_SIGMASK	5	/* restore signal mask in do_signal() */
 #define TIF_PERFMON_WORK	6	/* work for pfm_handle_work() */
+#define TIF_NEED_MIGRATE	7	/* migration necessary */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		17
 #define TIF_MCA_INIT		18	/* this task is processing MCA or INIT */

@@ -98,6 +101,7 @@ struct thread_info {
 #define _TIF_SYSCALL_TRACEAUDIT	(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SINGLESTEP)
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
 #define _TIF_PERFMON_WORK	(1 << TIF_PERFMON_WORK)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)

include/asm-m32r/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-m32r/thread_info.h
===================================================================
@@ -29,6 +29,7 @@ struct thread_info {
 	unsigned long		status;		/* thread-synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user-thread

@@ -69,6 +70,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\

@@ -150,6 +152,7 @@ static inline unsigned int get_thread_fa
 #define TIF_NEED_RESCHED	2	/* rescheduling necessary */
 #define TIF_SINGLESTEP		3	/* restore singlestep on return to user mode */
 #define TIF_IRET		4	/* return with iret */
+#define TIF_NEED_MIGRATE	5	/* migration necessary */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 					/* 31..28 fault code */
 #define TIF_MEMDIE		17

@@ -160,6 +163,7 @@ static inline unsigned int get_thread_fa
 #define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
 #define _TIF_IRET		(1<<TIF_IRET)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */
 #define _TIF_ALLWORK_MASK	0x0000FFFF	/* work to do on any return to u-space */

include/asm-m68k/thread_info.h +2 -0

Index: linux-2.6-lttng/include/asm-m68k/thread_info.h
===================================================================
@@ -9,6 +9,7 @@ struct thread_info {
 	unsigned long		flags;
 	struct exec_domain	*exec_domain;	/* execution domain */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	__u32 cpu; /* should always be 0 on m68k */
 	struct restart_block    restart_block;
 };

@@ -59,5 +60,6 @@ struct thread_info {
 #define TIF_DELAYED_TRACE	14	/* single step a syscall */
 #define TIF_SYSCALL_TRACE	15	/* syscall trace active */
 #define TIF_MEMDIE		16
+#define TIF_NEED_MIGRATE	17	/* migration necessary */
 
 #endif	/* _ASM_M68K_THREAD_INFO_H */

include/asm-m68knommu/thread_info.h +3 -0

Index: linux-2.6-lttng/include/asm-m68knommu/thread_info.h
===================================================================
@@ -37,6 +37,7 @@ struct thread_info {
 	unsigned long	   flags;		/* low level flags */
 	int		   cpu;			/* cpu we're on */
 	int		   preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int		   migrate_count;	/* 0: can migrate, <0 => BUG */
 	struct restart_block restart_block;
 };

@@ -88,6 +89,7 @@ static inline struct thread_info *curren
 #define TIF_POLLING_NRFLAG	3	/* true if poll_idle() is polling
 					   TIF_NEED_RESCHED */
 #define TIF_MEMDIE		4
+#define TIF_NEED_MIGRATE	5	/* migration necessary */
 #define	TIF_SYSCALL_AUDIT	7	/* syscall auditing active */
 
 /* as above, but as bit values */

@@ -96,6 +98,7 @@ static inline struct thread_info *curren
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_MEMDIE		(1<<TIF_MEMDIE)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */

include/asm-mips/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-mips/thread_info.h
===================================================================
@@ -28,6 +28,7 @@ struct thread_info {
 	unsigned long		tp_value;	/* thread pointer */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space:
 						   0-0xBFFFFFFF for user-thead

@@ -49,6 +50,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\

@@ -113,6 +115,7 @@ register struct thread_info *__current_t
 #define TIF_NEED_RESCHED	2	/* rescheduling necessary */
 #define TIF_SYSCALL_AUDIT	3	/* syscall auditing active */
 #define TIF_SECCOMP		4	/* secure computing */
+#define TIF_NEED_MIGRATE	5	/* migration necessary */
 #define TIF_RESTORE_SIGMASK	9	/* restore signal mask in do_signal() */
 #define TIF_USEDFPU		16	/* FPU was used by this task this quantum (SMP) */
 #define TIF_POLLING_NRFLAG	17	/* true if poll_idle() is polling TIF_NEED_RESCHED */

@@ -125,6 +128,7 @@ register struct thread_info *__current_t
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 #define _TIF_USEDFPU		(1<<TIF_USEDFPU)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)

include/asm-parisc/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-parisc/thread_info.h
===================================================================
@@ -13,6 +13,7 @@ struct thread_info {
 	mm_segment_t addr_limit;	/* user-level address space limit */
 	__u32 cpu;			/* current CPU */
 	int preempt_count;		/* 0=premptable, <0=BUG; will also serve as bh-counter */
+	int migrate_count;		/* 0: can migrate, <0 => BUG */
 	struct restart_block restart_block;
 };

@@ -24,6 +25,7 @@ struct thread_info {
 	.cpu		= 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
   	.restart_block	= {			\
 		.fn = do_no_restart_syscall	\
 	}					\

@@ -62,6 +64,7 @@ struct thread_info {
 #define TIF_32BIT               4       /* 32 bit binary */
 #define TIF_MEMDIE		5
 #define TIF_RESTORE_SIGMASK	6	/* restore saved signal mask */
+#define TIF_NEED_MIGRATE	7	/* migration necessary */
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)

@@ -69,6 +72,7 @@ struct thread_info {
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)
 #define _TIF_32BIT		(1 << TIF_32BIT)
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 
 #define _TIF_USER_WORK_MASK     (_TIF_SIGPENDING | \
                                  _TIF_NEED_RESCHED | _TIF_RESTORE_SIGMASK)

include/asm-powerpc/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-powerpc/thread_info.h
===================================================================
@@ -35,6 +35,7 @@ struct thread_info {
 	int		cpu;			/* cpu we're on */
 	int		preempt_count;		/* 0 => preemptable,
 						   <0 => BUG */
+	int		migrate_count;	/* 0: can migrate, <0 => BUG */
 	struct restart_block restart_block;
 	unsigned long	local_flags;		/* private flags for thread */

@@ -53,6 +54,7 @@ struct thread_info {
 	.exec_domain =	&default_exec_domain,	\
 	.cpu =		0,			\
 	.preempt_count = 1,			\
+	.migrate_count = 0,			\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\
 	},					\

@@ -124,6 +126,7 @@ static inline struct thread_info *curren
 #define TIF_FREEZE		14	/* Freezing for suspend */
 #define TIF_RUNLATCH		15	/* Is the runlatch enabled? */
 #define TIF_ABI_PENDING		16	/* 32/64 bit switch needed */
+#define TIF_NEED_MIGRATE	17	/* migration necessary */
 
 /* as above, but as bit values */
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)

@@ -142,6 +145,7 @@ static inline struct thread_info *curren
 #define _TIF_FREEZE		(1<<TIF_FREEZE)
 #define _TIF_RUNLATCH		(1<<TIF_RUNLATCH)
 #define _TIF_ABI_PENDING	(1<<TIF_ABI_PENDING)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_SYSCALL_T_OR_A	(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SECCOMP)
 
 #define _TIF_USER_WORK_MASK	( _TIF_SIGPENDING | \

include/asm-s390/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-s390/thread_info.h
===================================================================
@@ -51,6 +51,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	unsigned int		cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	struct restart_block	restart_block;
 };

@@ -64,6 +65,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\
 	},					\

@@ -96,6 +98,7 @@ static inline struct thread_info *curren
 #define TIF_SYSCALL_AUDIT	5	/* syscall auditing active */
 #define TIF_SINGLE_STEP		6	/* deliver sigtrap on return to user */
 #define TIF_MCCK_PENDING	7	/* machine check handling is pending */
+#define TIF_NEED_MIGRATE	8	/* migration necessary */
 #define TIF_USEDFPU		16	/* FPU was used by this task this quantum (SMP) */
 #define TIF_POLLING_NRFLAG	17	/* true if poll_idle() is polling 
 					   TIF_NEED_RESCHED */

@@ -110,6 +113,7 @@ static inline struct thread_info *curren
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_SINGLE_STEP	(1<<TIF_SINGLE_STEP)
 #define _TIF_MCCK_PENDING	(1<<TIF_MCCK_PENDING)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_USEDFPU		(1<<TIF_USEDFPU)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_31BIT		(1<<TIF_31BIT)

include/asm-sh/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-sh/thread_info.h
===================================================================
@@ -21,6 +21,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	__u32			cpu;
 	int			preempt_count; /* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	mm_segment_t		addr_limit;	/* thread address space */
 	struct restart_block	restart_block;
 	unsigned long		previous_sp;	/* sp of previous stack in case

@@ -58,6 +59,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\

@@ -112,6 +114,7 @@ static inline struct thread_info *curren
 #define TIF_RESTORE_SIGMASK	3	/* restore signal mask in do_signal() */
 #define TIF_SINGLESTEP		4	/* singlestepping active */
 #define	TIF_SYSCALL_AUDIT	6	/* syscall audit active */
+#define TIF_NEED_MIGRATE	7	/* migration necessary */
 #define TIF_USEDFPU		16	/* FPU was used by this task this quantum (SMP) */
 #define TIF_POLLING_NRFLAG	17	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		18

@@ -123,6 +126,7 @@ static inline struct thread_info *curren
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 #define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_USEDFPU		(1<<TIF_USEDFPU)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_FREEZE		(1<<TIF_FREEZE)

include/asm-sh64/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-sh64/thread_info.h
===================================================================
@@ -23,6 +23,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	/* Put the 4 32-bit fields together to make asm offsetting easier. */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	__u16			cpu;
 
 	mm_segment_t		addr_limit;

@@ -41,6 +42,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit     = KERNEL_DS,            \
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\

@@ -80,12 +82,14 @@ static inline struct thread_info *curren
 #define TIF_NEED_RESCHED	3	/* rescheduling necessary */
 #define TIF_MEMDIE		4
 #define TIF_RESTORE_SIGMASK	5	/* Restore signal mask in do_signal */
+#define TIF_NEED_MIGRATE	6	/* migration necessary */
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
 #define _TIF_MEMDIE		(1 << TIF_MEMDIE)
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 
 #endif /* __KERNEL__ */

include/asm-sparc/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-sparc/thread_info.h
===================================================================
@@ -33,6 +33,7 @@ struct thread_info {
 	int			cpu;		/* cpu we're on */
 	int			preempt_count;	/* 0 => preemptable,
 						   <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	int			softirq_count;
 	int			hardirq_count;

@@ -65,6 +66,7 @@ struct thread_info {
 	.flags		=	0,			\
 	.cpu		=	0,			\
 	.preempt_count	=	1,			\
+	.migrate_count =	0,			\
 	.restart_block	= {				\
 		.fn	=	do_no_restart_syscall,	\
 	},						\

@@ -132,6 +134,7 @@ BTFIXUPDEF_CALL(void, free_thread_info, 
 #define TIF_SIGPENDING		2	/* signal pending */
 #define TIF_NEED_RESCHED	3	/* rescheduling necessary */
 #define TIF_RESTORE_SIGMASK	4	/* restore signal mask in do_signal() */
+#define TIF_NEED_MIGRATE	5	/* migration necessary */
 #define TIF_USEDFPU		8	/* FPU was used by this task
 					 * this quantum (SMP) */
 #define TIF_POLLING_NRFLAG	9	/* true if poll_idle() is polling

@@ -144,6 +147,7 @@ BTFIXUPDEF_CALL(void, free_thread_info, 
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_USEDFPU		(1<<TIF_USEDFPU)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)

include/asm-sparc64/thread_info.h +4 -1

Index: linux-2.6-lttng/include/asm-sparc64/thread_info.h
===================================================================
@@ -47,6 +47,7 @@ struct thread_info {
 	struct pt_regs		*kregs;
 	struct exec_domain	*exec_domain;
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	__u8			new_child;
 	__u8			syscall_noerror;
 	__u16			cpu;

@@ -137,6 +138,7 @@ struct thread_info {
 	.flags		= ((unsigned long)ASI_P) << TI_FLAG_CURRENT_DS_SHIFT,	\
 	.exec_domain	=	&default_exec_domain,	\
 	.preempt_count	=	1,			\
+	.migrate_count =	0,			\
 	.restart_block	= {				\
 		.fn	=	do_no_restart_syscall,	\
 	},						\

@@ -225,7 +227,7 @@ register struct thread_info *current_thr
 #define TIF_UNALIGNED		5	/* allowed to do unaligned accesses */
 #define TIF_NEWSIGNALS		6	/* wants new-style signals */
 #define TIF_32BIT		7	/* 32-bit binary */
-/* flag bit 8 is available */
+#define TIF_NEED_MIGRATE	8	/* migration necessary */
 #define TIF_SECCOMP		9	/* secure computing */
 #define TIF_SYSCALL_AUDIT	10	/* syscall auditing active */
 /* flag bit 11 is available */

@@ -244,6 +246,7 @@ register struct thread_info *current_thr
 #define _TIF_UNALIGNED		(1<<TIF_UNALIGNED)
 #define _TIF_NEWSIGNALS		(1<<TIF_NEWSIGNALS)
 #define _TIF_32BIT		(1<<TIF_32BIT)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)

include/asm-um/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-um/thread_info.h
===================================================================
@@ -18,6 +18,7 @@ struct thread_info {
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;  /* 0 => preemptable,
 						   <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user
 						   0-0xFFFFFFFF for kernel */

@@ -32,6 +33,7 @@ struct thread_info {
 	.flags =		0,		\
 	.cpu =		0,			\
 	.preempt_count =	1,		\
+	.migrate_count =	0,		\
 	.addr_limit =	KERNEL_DS,		\
 	.restart_block =  {			\
 		.fn =  do_no_restart_syscall,	\

@@ -82,6 +84,7 @@ static inline struct thread_info *curren
 #define TIF_MEMDIE	 	5
 #define TIF_SYSCALL_AUDIT	6
 #define TIF_RESTORE_SIGMASK	7
+#define TIF_NEED_MIGRATE	8	/* migration necessary */
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)

@@ -90,5 +93,6 @@ static inline struct thread_info *curren
 #define _TIF_MEMDIE		(1 << TIF_MEMDIE)
 #define _TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 
 #endif

include/asm-v850/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-v850/thread_info.h
===================================================================
@@ -32,6 +32,7 @@ struct thread_info {
 	int			cpu;		/* cpu we're on */
 	int			preempt_count;	/* 0 => preemptable,
 						   <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	struct restart_block	restart_block;
 };

@@ -42,6 +43,7 @@ struct thread_info {
 	.flags =	0,						      \
 	.cpu =		0,						      \
 	.preempt_count = 1,						      \
+	.migrate_count = 0,						      \
 	.restart_block = {						      \
 		.fn = do_no_restart_syscall,				      \
 	},								      \

@@ -82,12 +84,14 @@ struct thread_info {
 #define TIF_POLLING_NRFLAG	3	/* true if poll_idle() is polling
 					   TIF_NEED_RESCHED */
 #define TIF_MEMDIE		4
+#define TIF_NEED_MIGRATE	5	/* migration necessary */
 
 /* as above, but as bit values */
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 
 /* Size of kernel stack for each process.  */

include/asm-x86_64/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-x86_64/thread_info.h
===================================================================
@@ -30,6 +30,7 @@ struct thread_info {
 	__u32			status;		/* thread synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int 			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	
 	struct restart_block    restart_block;

@@ -48,6 +49,7 @@ struct thread_info {
 	.flags	       = 0,			\
 	.cpu	       = 0,			\
 	.preempt_count = 1,			\
+	.migrate_count = 0,			\
 	.addr_limit     = KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\

@@ -115,6 +117,7 @@ static inline struct thread_info *stack_
 #define TIF_SECCOMP		8	/* secure computing */
 #define TIF_RESTORE_SIGMASK	9	/* restore signal mask in do_signal */
 #define TIF_MCE_NOTIFY		10	/* notify userspace of an MCE */
+#define TIF_NEED_MIGRATE	11	/* migration necessary */
 /* 16 free */
 #define TIF_IA32		17	/* 32bit process */ 
 #define TIF_FORK		18	/* ret_from_fork */

@@ -133,6 +136,7 @@ static inline struct thread_info *stack_
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 #define _TIF_MCE_NOTIFY		(1<<TIF_MCE_NOTIFY)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_IA32		(1<<TIF_IA32)
 #define _TIF_FORK		(1<<TIF_FORK)
 #define _TIF_ABI_PENDING	(1<<TIF_ABI_PENDING)

include/asm-xtensa/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-xtensa/thread_info.h
===================================================================
@@ -34,6 +34,7 @@ struct thread_info {
 	unsigned long		status;		/* thread-synchronous flags */
 	__u32			cpu;		/* current CPU */
 	__s32			preempt_count;	/* 0 => preemptable,< 0 => BUG*/
+	__s32			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space */
 	struct restart_block    restart_block;

@@ -72,6 +73,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\

@@ -116,6 +118,7 @@ static inline struct thread_info *curren
 #define TIF_IRET		4	/* return with iret */
 #define TIF_MEMDIE		5
 #define TIF_RESTORE_SIGMASK	6	/* restore signal mask in do_signal() */
+#define TIF_NEED_MIGRATE	7	/* migration necessary */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)

@@ -123,6 +126,7 @@ static inline struct thread_info *curren
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
 #define _TIF_IRET		(1<<TIF_IRET)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)

lib/smp_processor_id.c +5 -1

Index: linux-2.6-lttng/lib/smp_processor_id.c
===================================================================
@@ -10,12 +10,16 @@
 unsigned int debug_smp_processor_id(void)
 {
 	unsigned long preempt_count = preempt_count();
+	unsigned long migrate_count = migrate_count();
 	int this_cpu = raw_smp_processor_id();
 	cpumask_t this_mask;
 
 	if (likely(preempt_count))
 		goto out;
 
+	if (likely(migrate_count))
+		goto out;
+
 	if (irqs_disabled())
 		goto out;

@@ -42,7 +46,7 @@ unsigned int debug_smp_processor_id(void
 	if (!printk_ratelimit())
 		goto out_enable;
 
-	printk(KERN_ERR "BUG: using smp_processor_id() in preemptible [%08x] code: %s/%d\n", preempt_count(), current->comm, current->pid);
+	printk(KERN_ERR "BUG: using smp_processor_id() in preemptible [%08x] migration [%08x] code: %s/%d\n", preempt_count(), migrate_count(), current->comm, current->pid);
 	print_symbol("caller is %s\n", (long)__builtin_return_address(0));
 	dump_stack();

Signature · 3 lines

Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

Mathieu Desnoyers

2007-07-14 18:42 UTC #8 lore raw

RFC 1/1 Thread Migration Preemption - v4

In reply to Oleg Nesterov

Thread Migration Preemption

(v3 did not have the latest updates from Oleg review)

This patch adds the ability to protect critical sections from migration to another CPU without disabling preemption.

Typical use:

migrate_disable();
local_inc(&__get_cpu_var(&my_local_t_var));
migrate_enable();

Which will increment the variable atomically wrt the local CPU.

Changes:

Do a check_migrate() upon migrate_enable() to answer to the migration thread waiting for us to exit the migration disabled critical section. Use a NEED_MIGRATE thread flag for this.

FIXME (HOTPLUG) :

Quoted 4 lines

    /* Affinity changed (again). */
    if (!cpu_isset(dest_cpu, p->cpus_allowed))
            goto out;

Quoted 12 lines

Review
Quoted 5 lines
    on_rq = p->se.on_rq;
(quoted diff) +4 -0
+#ifdef CONFIG_PREEMPT
+   if (!on_rq && task_thread_info(p)->migrate_count)
+           goto out;
+#endif
This means that move_task_off_dead_cpu() will spin until the task will be scheduled
on the dead CPU. Given that we hold tasklist_lock and irqs are disabled, this may
never happen.

Yes. My idea to fix this issue is the following:

(I'll wait for reply before coding a solution for this CPU HOTPLUG related problem)

Signed-off-by Mathieu Desnoyers <[email protected]>

---
 include/asm-alpha/thread_info.h     |    3 +
 include/asm-arm/thread_info.h       |    5 +
 include/asm-arm26/thread_info.h     |    5 +
 include/asm-avr32/thread_info.h     |    4 +
 include/asm-blackfin/thread_info.h  |    4 +
 include/asm-cris/thread_info.h      |    4 +
 include/asm-frv/thread_info.h       |    4 +
 include/asm-h8300/thread_info.h     |    4 +
 include/asm-i386/thread_info.h      |    6 +-
 include/asm-ia64/thread_info.h      |    4 +
 include/asm-m32r/thread_info.h      |    4 +
 include/asm-m68k/thread_info.h      |    2 
 include/asm-m68knommu/thread_info.h |    3 +
 include/asm-mips/thread_info.h      |    4 +
 include/asm-parisc/thread_info.h    |    4 +
 include/asm-powerpc/thread_info.h   |    4 +
 include/asm-s390/thread_info.h      |    4 +
 include/asm-sh/thread_info.h        |    4 +
 include/asm-sh64/thread_info.h      |    4 +
 include/asm-sparc/thread_info.h     |    4 +
 include/asm-sparc64/thread_info.h   |    5 +
 include/asm-um/thread_info.h        |    4 +
 include/asm-v850/thread_info.h      |    4 +
 include/asm-x86_64/thread_info.h    |    4 +
 include/asm-xtensa/thread_info.h    |    4 +
 include/linux/preempt.h             |   47 ++++++++++++++++
 kernel/sched.c                      |  103 +++++++++++++++++++++++++++++++++---
 lib/smp_processor_id.c              |    6 +-
 28 files changed, 245 insertions(+), 12 deletions(-)

include/asm-i386/thread_info.h +4 -2

Index: linux-2.6-lttng/include/asm-i386/thread_info.h
===================================================================
@@ -31,8 +31,7 @@ struct thread_info {
 	unsigned long		status;		/* thread-synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
-
-
+	int			migrate_count;/* 0: can migrate, <0: BUG */
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user-thead
 						   0-0xFFFFFFFF for kernel-thread

@@ -74,6 +73,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\

@@ -132,6 +132,7 @@ static inline struct thread_info *curren
 #define TIF_SYSCALL_AUDIT	6	/* syscall auditing active */
 #define TIF_SECCOMP		7	/* secure computing */
 #define TIF_RESTORE_SIGMASK	8	/* restore signal mask in do_signal() */
+#define TIF_NEED_MIGRATE	9	/* migration necessary */
 #define TIF_MEMDIE		16
 #define TIF_DEBUG		17	/* uses debug registers */
 #define TIF_IO_BITMAP		18	/* uses I/O bitmap */

@@ -147,6 +148,7 @@ static inline struct thread_info *curren
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_DEBUG		(1<<TIF_DEBUG)
 #define _TIF_IO_BITMAP		(1<<TIF_IO_BITMAP)
 #define _TIF_FREEZE		(1<<TIF_FREEZE)

include/linux/preempt.h +46 -1

73 lines not on this page · raw message

kernel/sched.c +96 -7

182 lines not on this page · raw message

include/asm-alpha/thread_info.h +3 -0

Index: linux-2.6-lttng/include/asm-alpha/thread_info.h
===================================================================
@@ -21,6 +21,7 @@ struct thread_info {
 	mm_segment_t		addr_limit;	/* thread address space */
 	unsigned		cpu;		/* current CPU */
 	int			preempt_count; /* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	int bpt_nsaved;
 	unsigned long bpt_addr[2];		/* breakpoint handling  */

@@ -77,6 +78,7 @@ register struct thread_info *__current_t
 #define TIF_MEMDIE		8
 #define TIF_RESTORE_SIGMASK	9	/* restore signal mask in do_signal */
 #define	TIF_SYSCALL_AUDIT	10
+#define TIF_NEED_MIGRATE	11	/* migration necessary */
 
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)

@@ -84,6 +86,7 @@ register struct thread_info *__current_t
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 /* Work to do on interrupt/exception return.  */
 #define _TIF_WORK_MASK		(_TIF_SIGPENDING | _TIF_NEED_RESCHED)

include/asm-arm/thread_info.h +5 -0

Index: linux-2.6-lttng/include/asm-arm/thread_info.h
===================================================================
@@ -51,6 +51,7 @@ struct cpu_context_save {
 struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	int			preempt_count;	/* 0 => preemptable, <0 => bug */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	mm_segment_t		addr_limit;	/* address limit */
 	struct task_struct	*task;		/* main task structure */
 	struct exec_domain	*exec_domain;	/* execution domain */

@@ -72,6 +73,7 @@ struct thread_info {
 	.exec_domain	= &default_exec_domain,				\
 	.flags		= 0,						\
 	.preempt_count	= 1,						\
+	.migrate_count = 0,						\
 	.addr_limit	= KERNEL_DS,					\
 	.cpu_domain	= domain_val(DOMAIN_USER, DOMAIN_MANAGER) |	\
 			  domain_val(DOMAIN_KERNEL, DOMAIN_MANAGER) |	\

@@ -137,12 +139,14 @@ extern void iwmmxt_task_switch(struct th
  *  TIF_SYSCALL_TRACE	- syscall trace active
  *  TIF_SIGPENDING	- signal pending
  *  TIF_NEED_RESCHED	- rescheduling necessary
+ *  TIF_NEED_MIGRATE	- migration necessary
  *  TIF_USEDFPU		- FPU was used by this task this quantum (SMP)
  *  TIF_POLLING_NRFLAG	- true if poll_idle() is polling TIF_NEED_RESCHED
  *  TIF_SYSCALL_AUDIT	- Syscall audting active - LTTng
  */
 #define TIF_SIGPENDING		0
 #define TIF_NEED_RESCHED	1
+#define TIF_NEED_MIGRATE	2
 #define	TIF_SYSCALL_AUDIT	7
 #define TIF_SYSCALL_TRACE	8
 #define TIF_POLLING_NRFLAG	16

@@ -152,6 +156,7 @@ extern void iwmmxt_task_switch(struct th
 
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define	_TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)

include/asm-arm26/thread_info.h +5 -0

Index: linux-2.6-lttng/include/asm-arm26/thread_info.h
===================================================================
@@ -45,6 +45,7 @@ struct cpu_context_save {
 struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	int			preempt_count;	/* 0 => preemptable, <0 => bug */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	mm_segment_t		addr_limit;	/* address limit */
 	struct task_struct	*task;		/* main task structure */
 	struct exec_domain      *exec_domain;   /* execution domain */

@@ -60,6 +61,7 @@ struct thread_info {
 	.exec_domain	&default_exec_domain,	\
 	.flags		0,			\
 	.preempt_count	0,			\
+	.migrate_count 0,			\
 	.addr_limit	KERNEL_DS,		\
 	.restart_block  = {                             \
 		.fn     = do_no_restart_syscall,        \

@@ -112,11 +114,13 @@ extern void free_thread_info(struct thre
  *  TIF_SYSCALL_TRACE	- syscall trace active
  *  TIF_SIGPENDING	- signal pending
  *  TIF_NEED_RESCHED	- rescheduling necessary
+ *  TIF_NEED_MIGRATE	- migration necessary
  *  TIF_USEDFPU		- FPU was used by this task this quantum (SMP)
  *  TIF_POLLING_NRFLAG	- true if poll_idle() is polling TIF_NEED_RESCHED
  */
 #define TIF_SIGPENDING		0
 #define TIF_NEED_RESCHED	1
+#define TIF_NEED_MIGRATE	2
 #define TIF_SYSCALL_TRACE	8
 #define TIF_USED_FPU		16
 #define TIF_POLLING_NRFLAG	17

@@ -124,6 +128,7 @@ extern void free_thread_info(struct thre
 
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_USED_FPU		(1 << TIF_USED_FPU)
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)

include/asm-avr32/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-avr32/thread_info.h
===================================================================
@@ -25,6 +25,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	__u32			cpu;
 	__s32			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	struct restart_block	restart_block;
 	__u8			supervisor_stack[0];
 };

@@ -36,6 +37,7 @@ struct thread_info {
 	.flags		= 0,						\
 	.cpu		= 0,						\
 	.preempt_count	= 1,						\
+	.migrate_count = 0,						\
 	.restart_block	= {						\
 		.fn	= do_no_restart_syscall				\
 	}								\

@@ -83,6 +85,7 @@ static inline struct thread_info *curren
 #define TIF_MEMDIE		6
 #define TIF_RESTORE_SIGMASK	7	/* restore signal mask in do_signal */
 #define TIF_CPU_GOING_TO_SLEEP	8	/* CPU is entering sleep 0 mode */
+#define TIF_NEED_MIGRATE      9       /* migration necessary */
 #define TIF_USERSPACE		31      /* true if FS sets userspace */
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)

@@ -94,6 +97,7 @@ static inline struct thread_info *curren
 #define _TIF_MEMDIE		(1 << TIF_MEMDIE)
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
 #define _TIF_CPU_GOING_TO_SLEEP (1 << TIF_CPU_GOING_TO_SLEEP)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 
 /* XXX: These two masks must never span more than 16 bits! */
 /* work to do on interrupt/exception return */

include/asm-blackfin/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-blackfin/thread_info.h
===================================================================
@@ -54,6 +54,7 @@ struct thread_info {
 	unsigned long flags;	/* low level flags */
 	int cpu;		/* cpu we're on */
 	int preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int migrate_count;	/* 0: can migrate, <0 => BUG */
 	mm_segment_t addr_limit;	/* address limit */
 	struct restart_block restart_block;
 	struct l1_scratch_task_info l1_task_info;

@@ -69,6 +70,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count  = 1,                    \
+	.migrate_count = 0,			\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\
 	},					\

@@ -125,6 +127,7 @@ static inline struct thread_info *curren
 #define TIF_MEMDIE              4
 #define TIF_RESTORE_SIGMASK	5	/* restore signal mask in do_signal() */
 #define TIF_FREEZE              6       /* is freezing for suspend */
+#define TIF_NEED_MIGRATE	7	/* migration necessary */
 
 /* as above, but as bit values */
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)

@@ -133,6 +136,7 @@ static inline struct thread_info *curren
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 #define _TIF_FREEZE             (1<<TIF_FREEZE)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */

include/asm-cris/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-cris/thread_info.h
===================================================================
@@ -32,6 +32,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user-thead

@@ -58,6 +59,7 @@ struct thread_info {
 	.flags		= 0,				\
 	.cpu		= 0,				\
 	.preempt_count	= 1,				\
+	.migrate_count = 0,				\
 	.addr_limit	= KERNEL_DS,			\
 	.restart_block = {				\
 		       .fn = do_no_restart_syscall,	\

@@ -81,6 +83,7 @@ struct thread_info {
 #define TIF_SYSCALL_TRACE	0	/* syscall trace active */
 #define TIF_SIGPENDING		1	/* signal pending */
 #define TIF_NEED_RESCHED	2	/* rescheduling necessary */
+#define TIF_NEED_MIGRATE	3	/* migration necessary */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		17

@@ -88,6 +91,7 @@ struct thread_info {
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */
 #define _TIF_ALLWORK_MASK	0x0000FFFF	/* work to do on any return to u-space */

include/asm-frv/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-frv/thread_info.h
===================================================================
@@ -36,6 +36,7 @@ struct thread_info {
 	unsigned long		status;		/* thread-synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user-thead

@@ -68,6 +69,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\

@@ -113,6 +115,7 @@ register struct thread_info *__current_t
 #define TIF_SINGLESTEP		3	/* restore singlestep on return to user mode */
 #define TIF_IRET		4	/* return with iret */
 #define TIF_RESTORE_SIGMASK	5	/* restore signal mask in do_signal() */
+#define TIF_NEED_MIGRATE	6	/* migration necessary */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		17	/* OOM killer killed process */
 #define TIF_FREEZE		18	/* freezing for suspend */

@@ -125,6 +128,7 @@ register struct thread_info *__current_t
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)
 #define _TIF_FREEZE		(1 << TIF_FREEZE)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */
 #define _TIF_ALLWORK_MASK	0x0000FFFF	/* work to do on any return to u-space */

include/asm-h8300/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-h8300/thread_info.h
===================================================================
@@ -24,6 +24,7 @@ struct thread_info {
 	unsigned long	   flags;		/* low level flags */
 	int		   cpu;			/* cpu we're on */
 	int		   preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	struct restart_block restart_block;
 };

@@ -37,6 +38,7 @@ struct thread_info {
 	.flags =	0,			\
 	.cpu =		0,			\
 	.preempt_count = 1,			\
+	.migrate_count = 0,			\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\
 	},					\

@@ -91,12 +93,14 @@ static inline struct thread_info *curren
 #define TIF_POLLING_NRFLAG	3	/* true if poll_idle() is polling
 					   TIF_NEED_RESCHED */
 #define TIF_MEMDIE		4
+#define TIF_NEED_MIGRATE	5	/* migration necessary */
 
 /* as above, but as bit values */
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */

include/asm-ia64/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-ia64/thread_info.h
===================================================================
@@ -30,6 +30,7 @@ struct thread_info {
 	__u32 status;			/* Thread synchronous flags */
 	mm_segment_t addr_limit;	/* user-level address space limit */
 	int preempt_count;		/* 0=premptable, <0=BUG; will also serve as bh-counter */
+	int migrate_count;		/* 0: can migrate, <0 => BUG */
 	struct restart_block restart_block;
 };

@@ -43,6 +44,7 @@ struct thread_info {
 	.cpu		= 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.preempt_count	= 0,			\
+	.migrate_count = 0,			\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\
 	},					\

@@ -86,6 +88,7 @@ struct thread_info {
 #define TIF_SINGLESTEP		4	/* restore singlestep on return to user mode */
 #define TIF_RESTORE_SIGMASK	5	/* restore signal mask in do_signal() */
 #define TIF_PERFMON_WORK	6	/* work for pfm_handle_work() */
+#define TIF_NEED_MIGRATE	7	/* migration necessary */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		17
 #define TIF_MCA_INIT		18	/* this task is processing MCA or INIT */

@@ -98,6 +101,7 @@ struct thread_info {
 #define _TIF_SYSCALL_TRACEAUDIT	(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SINGLESTEP)
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
 #define _TIF_PERFMON_WORK	(1 << TIF_PERFMON_WORK)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)

include/asm-m32r/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-m32r/thread_info.h
===================================================================
@@ -29,6 +29,7 @@ struct thread_info {
 	unsigned long		status;		/* thread-synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user-thread

@@ -69,6 +70,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\

@@ -150,6 +152,7 @@ static inline unsigned int get_thread_fa
 #define TIF_NEED_RESCHED	2	/* rescheduling necessary */
 #define TIF_SINGLESTEP		3	/* restore singlestep on return to user mode */
 #define TIF_IRET		4	/* return with iret */
+#define TIF_NEED_MIGRATE	5	/* migration necessary */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 					/* 31..28 fault code */
 #define TIF_MEMDIE		17

@@ -160,6 +163,7 @@ static inline unsigned int get_thread_fa
 #define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
 #define _TIF_IRET		(1<<TIF_IRET)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */
 #define _TIF_ALLWORK_MASK	0x0000FFFF	/* work to do on any return to u-space */

include/asm-m68k/thread_info.h +2 -0

Index: linux-2.6-lttng/include/asm-m68k/thread_info.h
===================================================================
@@ -9,6 +9,7 @@ struct thread_info {
 	unsigned long		flags;
 	struct exec_domain	*exec_domain;	/* execution domain */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	__u32 cpu; /* should always be 0 on m68k */
 	struct restart_block    restart_block;
 };

@@ -59,5 +60,6 @@ struct thread_info {
 #define TIF_DELAYED_TRACE	14	/* single step a syscall */
 #define TIF_SYSCALL_TRACE	15	/* syscall trace active */
 #define TIF_MEMDIE		16
+#define TIF_NEED_MIGRATE	17	/* migration necessary */
 
 #endif	/* _ASM_M68K_THREAD_INFO_H */

include/asm-m68knommu/thread_info.h +3 -0

Index: linux-2.6-lttng/include/asm-m68knommu/thread_info.h
===================================================================
@@ -37,6 +37,7 @@ struct thread_info {
 	unsigned long	   flags;		/* low level flags */
 	int		   cpu;			/* cpu we're on */
 	int		   preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int		   migrate_count;	/* 0: can migrate, <0 => BUG */
 	struct restart_block restart_block;
 };

@@ -88,6 +89,7 @@ static inline struct thread_info *curren
 #define TIF_POLLING_NRFLAG	3	/* true if poll_idle() is polling
 					   TIF_NEED_RESCHED */
 #define TIF_MEMDIE		4
+#define TIF_NEED_MIGRATE	5	/* migration necessary */
 #define	TIF_SYSCALL_AUDIT	7	/* syscall auditing active */
 
 /* as above, but as bit values */

@@ -96,6 +98,7 @@ static inline struct thread_info *curren
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_MEMDIE		(1<<TIF_MEMDIE)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */

include/asm-mips/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-mips/thread_info.h
===================================================================
@@ -28,6 +28,7 @@ struct thread_info {
 	unsigned long		tp_value;	/* thread pointer */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space:
 						   0-0xBFFFFFFF for user-thead

@@ -49,6 +50,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\

@@ -113,6 +115,7 @@ register struct thread_info *__current_t
 #define TIF_NEED_RESCHED	2	/* rescheduling necessary */
 #define TIF_SYSCALL_AUDIT	3	/* syscall auditing active */
 #define TIF_SECCOMP		4	/* secure computing */
+#define TIF_NEED_MIGRATE	5	/* migration necessary */
 #define TIF_RESTORE_SIGMASK	9	/* restore signal mask in do_signal() */
 #define TIF_USEDFPU		16	/* FPU was used by this task this quantum (SMP) */
 #define TIF_POLLING_NRFLAG	17	/* true if poll_idle() is polling TIF_NEED_RESCHED */

@@ -125,6 +128,7 @@ register struct thread_info *__current_t
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 #define _TIF_USEDFPU		(1<<TIF_USEDFPU)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)

include/asm-parisc/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-parisc/thread_info.h
===================================================================
@@ -13,6 +13,7 @@ struct thread_info {
 	mm_segment_t addr_limit;	/* user-level address space limit */
 	__u32 cpu;			/* current CPU */
 	int preempt_count;		/* 0=premptable, <0=BUG; will also serve as bh-counter */
+	int migrate_count;		/* 0: can migrate, <0 => BUG */
 	struct restart_block restart_block;
 };

@@ -24,6 +25,7 @@ struct thread_info {
 	.cpu		= 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
   	.restart_block	= {			\
 		.fn = do_no_restart_syscall	\
 	}					\

@@ -62,6 +64,7 @@ struct thread_info {
 #define TIF_32BIT               4       /* 32 bit binary */
 #define TIF_MEMDIE		5
 #define TIF_RESTORE_SIGMASK	6	/* restore saved signal mask */
+#define TIF_NEED_MIGRATE	7	/* migration necessary */
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)

@@ -69,6 +72,7 @@ struct thread_info {
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)
 #define _TIF_32BIT		(1 << TIF_32BIT)
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 
 #define _TIF_USER_WORK_MASK     (_TIF_SIGPENDING | \
                                  _TIF_NEED_RESCHED | _TIF_RESTORE_SIGMASK)

include/asm-powerpc/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-powerpc/thread_info.h
===================================================================
@@ -35,6 +35,7 @@ struct thread_info {
 	int		cpu;			/* cpu we're on */
 	int		preempt_count;		/* 0 => preemptable,
 						   <0 => BUG */
+	int		migrate_count;	/* 0: can migrate, <0 => BUG */
 	struct restart_block restart_block;
 	unsigned long	local_flags;		/* private flags for thread */

@@ -53,6 +54,7 @@ struct thread_info {
 	.exec_domain =	&default_exec_domain,	\
 	.cpu =		0,			\
 	.preempt_count = 1,			\
+	.migrate_count = 0,			\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\
 	},					\

@@ -124,6 +126,7 @@ static inline struct thread_info *curren
 #define TIF_FREEZE		14	/* Freezing for suspend */
 #define TIF_RUNLATCH		15	/* Is the runlatch enabled? */
 #define TIF_ABI_PENDING		16	/* 32/64 bit switch needed */
+#define TIF_NEED_MIGRATE	17	/* migration necessary */
 
 /* as above, but as bit values */
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)

@@ -142,6 +145,7 @@ static inline struct thread_info *curren
 #define _TIF_FREEZE		(1<<TIF_FREEZE)
 #define _TIF_RUNLATCH		(1<<TIF_RUNLATCH)
 #define _TIF_ABI_PENDING	(1<<TIF_ABI_PENDING)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_SYSCALL_T_OR_A	(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SECCOMP)
 
 #define _TIF_USER_WORK_MASK	( _TIF_SIGPENDING | \

include/asm-s390/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-s390/thread_info.h
===================================================================
@@ -51,6 +51,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	unsigned int		cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	struct restart_block	restart_block;
 };

@@ -64,6 +65,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\
 	},					\

@@ -96,6 +98,7 @@ static inline struct thread_info *curren
 #define TIF_SYSCALL_AUDIT	5	/* syscall auditing active */
 #define TIF_SINGLE_STEP		6	/* deliver sigtrap on return to user */
 #define TIF_MCCK_PENDING	7	/* machine check handling is pending */
+#define TIF_NEED_MIGRATE	8	/* migration necessary */
 #define TIF_USEDFPU		16	/* FPU was used by this task this quantum (SMP) */
 #define TIF_POLLING_NRFLAG	17	/* true if poll_idle() is polling 
 					   TIF_NEED_RESCHED */

@@ -110,6 +113,7 @@ static inline struct thread_info *curren
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_SINGLE_STEP	(1<<TIF_SINGLE_STEP)
 #define _TIF_MCCK_PENDING	(1<<TIF_MCCK_PENDING)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_USEDFPU		(1<<TIF_USEDFPU)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_31BIT		(1<<TIF_31BIT)

include/asm-sh/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-sh/thread_info.h
===================================================================
@@ -21,6 +21,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	__u32			cpu;
 	int			preempt_count; /* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	mm_segment_t		addr_limit;	/* thread address space */
 	struct restart_block	restart_block;
 	unsigned long		previous_sp;	/* sp of previous stack in case

@@ -58,6 +59,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\

@@ -112,6 +114,7 @@ static inline struct thread_info *curren
 #define TIF_RESTORE_SIGMASK	3	/* restore signal mask in do_signal() */
 #define TIF_SINGLESTEP		4	/* singlestepping active */
 #define	TIF_SYSCALL_AUDIT	6	/* syscall audit active */
+#define TIF_NEED_MIGRATE	7	/* migration necessary */
 #define TIF_USEDFPU		16	/* FPU was used by this task this quantum (SMP) */
 #define TIF_POLLING_NRFLAG	17	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		18

@@ -123,6 +126,7 @@ static inline struct thread_info *curren
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 #define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_USEDFPU		(1<<TIF_USEDFPU)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_FREEZE		(1<<TIF_FREEZE)

include/asm-sh64/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-sh64/thread_info.h
===================================================================
@@ -23,6 +23,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	/* Put the 4 32-bit fields together to make asm offsetting easier. */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	__u16			cpu;
 
 	mm_segment_t		addr_limit;

@@ -41,6 +42,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit     = KERNEL_DS,            \
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\

@@ -80,12 +82,14 @@ static inline struct thread_info *curren
 #define TIF_NEED_RESCHED	3	/* rescheduling necessary */
 #define TIF_MEMDIE		4
 #define TIF_RESTORE_SIGMASK	5	/* Restore signal mask in do_signal */
+#define TIF_NEED_MIGRATE	6	/* migration necessary */
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
 #define _TIF_MEMDIE		(1 << TIF_MEMDIE)
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 
 #endif /* __KERNEL__ */

include/asm-sparc/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-sparc/thread_info.h
===================================================================
@@ -33,6 +33,7 @@ struct thread_info {
 	int			cpu;		/* cpu we're on */
 	int			preempt_count;	/* 0 => preemptable,
 						   <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	int			softirq_count;
 	int			hardirq_count;

@@ -65,6 +66,7 @@ struct thread_info {
 	.flags		=	0,			\
 	.cpu		=	0,			\
 	.preempt_count	=	1,			\
+	.migrate_count =	0,			\
 	.restart_block	= {				\
 		.fn	=	do_no_restart_syscall,	\
 	},						\

@@ -132,6 +134,7 @@ BTFIXUPDEF_CALL(void, free_thread_info, 
 #define TIF_SIGPENDING		2	/* signal pending */
 #define TIF_NEED_RESCHED	3	/* rescheduling necessary */
 #define TIF_RESTORE_SIGMASK	4	/* restore signal mask in do_signal() */
+#define TIF_NEED_MIGRATE	5	/* migration necessary */
 #define TIF_USEDFPU		8	/* FPU was used by this task
 					 * this quantum (SMP) */
 #define TIF_POLLING_NRFLAG	9	/* true if poll_idle() is polling

@@ -144,6 +147,7 @@ BTFIXUPDEF_CALL(void, free_thread_info, 
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_USEDFPU		(1<<TIF_USEDFPU)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)

include/asm-sparc64/thread_info.h +4 -1

Index: linux-2.6-lttng/include/asm-sparc64/thread_info.h
===================================================================
@@ -47,6 +47,7 @@ struct thread_info {
 	struct pt_regs		*kregs;
 	struct exec_domain	*exec_domain;
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	__u8			new_child;
 	__u8			syscall_noerror;
 	__u16			cpu;

@@ -137,6 +138,7 @@ struct thread_info {
 	.flags		= ((unsigned long)ASI_P) << TI_FLAG_CURRENT_DS_SHIFT,	\
 	.exec_domain	=	&default_exec_domain,	\
 	.preempt_count	=	1,			\
+	.migrate_count =	0,			\
 	.restart_block	= {				\
 		.fn	=	do_no_restart_syscall,	\
 	},						\

@@ -225,7 +227,7 @@ register struct thread_info *current_thr
 #define TIF_UNALIGNED		5	/* allowed to do unaligned accesses */
 #define TIF_NEWSIGNALS		6	/* wants new-style signals */
 #define TIF_32BIT		7	/* 32-bit binary */
-/* flag bit 8 is available */
+#define TIF_NEED_MIGRATE	8	/* migration necessary */
 #define TIF_SECCOMP		9	/* secure computing */
 #define TIF_SYSCALL_AUDIT	10	/* syscall auditing active */
 /* flag bit 11 is available */

@@ -244,6 +246,7 @@ register struct thread_info *current_thr
 #define _TIF_UNALIGNED		(1<<TIF_UNALIGNED)
 #define _TIF_NEWSIGNALS		(1<<TIF_NEWSIGNALS)
 #define _TIF_32BIT		(1<<TIF_32BIT)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)

include/asm-um/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-um/thread_info.h
===================================================================
@@ -18,6 +18,7 @@ struct thread_info {
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;  /* 0 => preemptable,
 						   <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user
 						   0-0xFFFFFFFF for kernel */

@@ -32,6 +33,7 @@ struct thread_info {
 	.flags =		0,		\
 	.cpu =		0,			\
 	.preempt_count =	1,		\
+	.migrate_count =	0,		\
 	.addr_limit =	KERNEL_DS,		\
 	.restart_block =  {			\
 		.fn =  do_no_restart_syscall,	\

@@ -82,6 +84,7 @@ static inline struct thread_info *curren
 #define TIF_MEMDIE	 	5
 #define TIF_SYSCALL_AUDIT	6
 #define TIF_RESTORE_SIGMASK	7
+#define TIF_NEED_MIGRATE	8	/* migration necessary */
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)

@@ -90,5 +93,6 @@ static inline struct thread_info *curren
 #define _TIF_MEMDIE		(1 << TIF_MEMDIE)
 #define _TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 
 #endif

include/asm-v850/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-v850/thread_info.h
===================================================================
@@ -32,6 +32,7 @@ struct thread_info {
 	int			cpu;		/* cpu we're on */
 	int			preempt_count;	/* 0 => preemptable,
 						   <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	struct restart_block	restart_block;
 };

@@ -42,6 +43,7 @@ struct thread_info {
 	.flags =	0,						      \
 	.cpu =		0,						      \
 	.preempt_count = 1,						      \
+	.migrate_count = 0,						      \
 	.restart_block = {						      \
 		.fn = do_no_restart_syscall,				      \
 	},								      \

@@ -82,12 +84,14 @@ struct thread_info {
 #define TIF_POLLING_NRFLAG	3	/* true if poll_idle() is polling
 					   TIF_NEED_RESCHED */
 #define TIF_MEMDIE		4
+#define TIF_NEED_MIGRATE	5	/* migration necessary */
 
 /* as above, but as bit values */
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 
 /* Size of kernel stack for each process.  */

include/asm-x86_64/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-x86_64/thread_info.h
===================================================================
@@ -30,6 +30,7 @@ struct thread_info {
 	__u32			status;		/* thread synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int 			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	
 	struct restart_block    restart_block;

@@ -48,6 +49,7 @@ struct thread_info {
 	.flags	       = 0,			\
 	.cpu	       = 0,			\
 	.preempt_count = 1,			\
+	.migrate_count = 0,			\
 	.addr_limit     = KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\

@@ -115,6 +117,7 @@ static inline struct thread_info *stack_
 #define TIF_SECCOMP		8	/* secure computing */
 #define TIF_RESTORE_SIGMASK	9	/* restore signal mask in do_signal */
 #define TIF_MCE_NOTIFY		10	/* notify userspace of an MCE */
+#define TIF_NEED_MIGRATE	11	/* migration necessary */
 /* 16 free */
 #define TIF_IA32		17	/* 32bit process */ 
 #define TIF_FORK		18	/* ret_from_fork */

@@ -133,6 +136,7 @@ static inline struct thread_info *stack_
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 #define _TIF_MCE_NOTIFY		(1<<TIF_MCE_NOTIFY)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_IA32		(1<<TIF_IA32)
 #define _TIF_FORK		(1<<TIF_FORK)
 #define _TIF_ABI_PENDING	(1<<TIF_ABI_PENDING)

include/asm-xtensa/thread_info.h +4 -0

Index: linux-2.6-lttng/include/asm-xtensa/thread_info.h
===================================================================
@@ -34,6 +34,7 @@ struct thread_info {
 	unsigned long		status;		/* thread-synchronous flags */
 	__u32			cpu;		/* current CPU */
 	__s32			preempt_count;	/* 0 => preemptable,< 0 => BUG*/
+	__s32			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space */
 	struct restart_block    restart_block;

@@ -72,6 +73,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\

@@ -116,6 +118,7 @@ static inline struct thread_info *curren
 #define TIF_IRET		4	/* return with iret */
 #define TIF_MEMDIE		5
 #define TIF_RESTORE_SIGMASK	6	/* restore signal mask in do_signal() */
+#define TIF_NEED_MIGRATE	7	/* migration necessary */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)

@@ -123,6 +126,7 @@ static inline struct thread_info *curren
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
 #define _TIF_IRET		(1<<TIF_IRET)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)

lib/smp_processor_id.c +5 -1

Index: linux-2.6-lttng/lib/smp_processor_id.c
===================================================================
@@ -10,12 +10,16 @@
 unsigned int debug_smp_processor_id(void)
 {
 	unsigned long preempt_count = preempt_count();
+	unsigned long migrate_count = migrate_count();
 	int this_cpu = raw_smp_processor_id();
 	cpumask_t this_mask;
 
 	if (likely(preempt_count))
 		goto out;
 
+	if (likely(migrate_count))
+		goto out;
+
 	if (irqs_disabled())
 		goto out;

@@ -42,7 +46,7 @@ unsigned int debug_smp_processor_id(void
 	if (!printk_ratelimit())
 		goto out_enable;
 
-	printk(KERN_ERR "BUG: using smp_processor_id() in preemptible [%08x] code: %s/%d\n", preempt_count(), current->comm, current->pid);
+	printk(KERN_ERR "BUG: using smp_processor_id() in preemptible [%08x] migration [%08x] code: %s/%d\n", preempt_count(), migrate_count(), current->comm, current->pid);
 	print_symbol("caller is %s\n", (long)__builtin_return_address(0));
 	dump_stack();

Signature · 3 lines

Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

Peter Zijlstra

2007-07-14 19:14 UTC #9 lore raw

Re: [RFC] Thread Migration Preemption - v4

Would have been nice if you'd CC'ed me :-/

Quoted 36 lines · Mathieu Desnoyers

kernel/sched.c +28 -3

@@ -4891,10 +4948,42 @@ static int migration_thread(void *data)
 		list_del_init(head->next);
 
 		spin_unlock(&rq->lock);
-		__migrate_task(req->task, cpu, req->dest_cpu);
+		migrated = __migrate_task(req->task, cpu, req->dest_cpu);
 		local_irq_enable();
-
-		complete(&req->done);
+		if (!migrated) {
+			/*
+			 * If the process has not been migrated, let it run
+			 * until it reaches a migration_check() so it can
+			 * wake us up.
+			 */
+			spin_lock_irq(&rq->lock);
+			head = &rq->migration_queue;
+			list_add(&req->list, head);
+			if (req->task->se.on_rq
+					|| !task_migrate_count(req->task)) {
+				/*
+				 * The process is on the runqueue, it could
+				 * exit its critical section at any moment,
+				 * don't race with it and retry actively.
+				 * Also, if the thread is not on the runqueue
+				 * and has a zero migration count
+				 * (__migrate_task failed because cpus allowed
+				 * changed), just retry.
+				 */
+				spin_unlock_irq(&rq->lock);
+				continue;
+			}
+			set_tsk_thread_flag(req->task, TIF_NEED_MIGRATE);
+			set_current_state(TASK_INTERRUPTIBLE);
+			spin_unlock_irq(&rq->lock);
+			/*

kernel/sched.c static int migration_thread(void *data) · line 4989

Quoted 10 lines

kernel/sched.c +7 -0

+			 * Wait for the process currently in its critical
+			 * section.
+			 */
+			wake_up_process(req->task);
+			schedule();
+		} else
+			complete(&req->done);
 	}
 	__set_current_state(TASK_RUNNING);
 	return 0;

I'm not really liking this, this way we hold up all other migration requests.

Mathieu Desnoyers

2007-07-14 20:25 UTC #10 lore raw

Re: [RFC] Thread Migration Preemption - v4

Quoted 2 lines · * Peter Zijlstra ([email protected]) wrote:

Would have been nice if you'd CC'ed me :-/

Sorry

Quoted 43 lines · Mathieu Desnoyers

Quoted 42 lines

kernel/sched.c +33 -3

@@ -4891,10 +4948,42 @@ static int migration_thread(void *data)
 		list_del_init(head->next);
 
 		spin_unlock(&rq->lock);
-		__migrate_task(req->task, cpu, req->dest_cpu);
+		migrated = __migrate_task(req->task, cpu, req->dest_cpu);
 		local_irq_enable();
-
-		complete(&req->done);
+		if (!migrated) {
+			/*
+			 * If the process has not been migrated, let it run
+			 * until it reaches a migration_check() so it can
+			 * wake us up.
+			 */
+			spin_lock_irq(&rq->lock);
+			head = &rq->migration_queue;
+			list_add(&req->list, head);
+			if (req->task->se.on_rq
+					|| !task_migrate_count(req->task)) {
+				/*
+				 * The process is on the runqueue, it could
+				 * exit its critical section at any moment,
+				 * don't race with it and retry actively.
+				 * Also, if the thread is not on the runqueue
+				 * and has a zero migration count
+				 * (__migrate_task failed because cpus allowed
+				 * changed), just retry.
+				 */
+				spin_unlock_irq(&rq->lock);
+				continue;
+			}
+			set_tsk_thread_flag(req->task, TIF_NEED_MIGRATE);
+			set_current_state(TASK_INTERRUPTIBLE);
+			spin_unlock_irq(&rq->lock);
+			/*
+			 * Wait for the process currently in its critical
+			 * section.
+			 */
+			wake_up_process(req->task);
+			schedule();

Quoted 9 lines

kernel/sched.c static int migration_thread(void *data) · line 4989
Quoted 5 lines
kernel/sched.c +2 -0
+		} else
+			complete(&req->done);
 	}
 	__set_current_state(TASK_RUNNING);
 	return 0;
I'm not really liking this, this way we hold up all other migration requests.

True. You approach of delayed migration helps on this.

Signature · 3 lines

Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

Peter Zijlstra

2007-07-14 19:30 UTC #11 lore raw

Re: [RFC] Thread Migration Preemption - v4

In reply to Mathieu Desnoyers

Quoted 32 lines · Mathieu Desnoyers

Note: (or we could say FIXME)
Is we ever want to check migration pending in assembly code, we will have to make sure we test the right thread flag bits on each architectures. Care should also be taken to check that the thread flags used won't trigger false positives in non selective asm thread flag checks.
FIXME (HOTPLUG) :
Quoted 4 lines
Quoted 4 lines
    /* Affinity changed (again). */
    if (!cpu_isset(dest_cpu, p->cpus_allowed))
            goto out;
Quoted 12 lines
Review
Quoted 5 lines
    on_rq = p->se.on_rq;
(quoted diff) +4 -0
+#ifdef CONFIG_PREEMPT
+   if (!on_rq && task_thread_info(p)->migrate_count)
+           goto out;
+#endif
This means that move_task_off_dead_cpu() will spin until the task will be scheduled
on the dead CPU. Given that we hold tasklist_lock and irqs are disabled, this may
never happen.
Yes. My idea to fix this issue is the following:
If a thread has non zero migrate_count, we should still move it to a different CPU upon hotplug cpu removal, even if this thread resists migration. Care should be taken to send _all_ such threads to the _same_ CPU so they don't race for the per-cpu ressources. Does it make sense ?

Quoted 7 lines

We would have to keep the CPU affinity of the threads running on the wrong CPU until they end their migrate disabled section, so that we can put them back on their original CPU if it goes back online, otherwise we could end up with concurrent per-cpu variables accesses.
(I'll wait for reply before coding a solution for this CPU HOTPLUG related problem)

What would, aside from technical issues, be the problem with making migration_disable() delay CPU_DOWN until migration_enable()?

Mathieu Desnoyers

2007-07-14 20:26 UTC #12 lore raw

Re: [RFC] Thread Migration Preemption - v4

Quoted 39 lines · * Peter Zijlstra ([email protected]) wrote:

Quoted 37 lines · Mathieu Desnoyers
Note: (or we could say FIXME)
Is we ever want to check migration pending in assembly code, we will have to make sure we test the right thread flag bits on each architectures. Care should also be taken to check that the thread flags used won't trigger false positives in non selective asm thread flag checks.
FIXME (HOTPLUG) :
Quoted 4 lines
Quoted 4 lines
    /* Affinity changed (again). */
    if (!cpu_isset(dest_cpu, p->cpus_allowed))
            goto out;
Quoted 12 lines
Review
Quoted 5 lines
    on_rq = p->se.on_rq;
(quoted diff) +4 -0
+#ifdef CONFIG_PREEMPT
+   if (!on_rq && task_thread_info(p)->migrate_count)
+           goto out;
+#endif
This means that move_task_off_dead_cpu() will spin until the task will be scheduled
on the dead CPU. Given that we hold tasklist_lock and irqs are disabled, this may
never happen.
Yes. My idea to fix this issue is the following:
If a thread has non zero migrate_count, we should still move it to a different CPU upon hotplug cpu removal, even if this thread resists migration. Care should be taken to send _all_ such threads to the _same_ CPU so they don't race for the per-cpu ressources. Does it make sense ?
We would have to keep the CPU affinity of the threads running on the wrong CPU until they end their migrate disabled section, so that we can put them back on their original CPU if it goes back online, otherwise we could end up with concurrent per-cpu variables accesses.

Quoted 6 lines

Quoted 2 lines
(I'll wait for reply before coding a solution for this CPU HOTPLUG related problem)
What would, aside from technical issues, be the problem with making migration_disable() delay CPU_DOWN until migration_enable()?

Because if we thing a little further, migration disabling could be a very interesting way to provide cheap per-cpu data structure access to user-space. But we would not want user-space processes to hold CPU_DOWN forever...

Signature · 3 lines

Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

Oleg Nesterov

author

2007-07-14 20:23 UTC #13 lore raw

Re: [RFC] Thread Migration Preemption - v4

In reply to Mathieu Desnoyers

Quoted 22 lines · Mathieu Desnoyers

kernel/sched.c +13 -3

@@ -4891,10 +4948,42 @@ static int migration_thread(void *data)
 		list_del_init(head->next);
 
 		spin_unlock(&rq->lock);
-		__migrate_task(req->task, cpu, req->dest_cpu);
+		migrated = __migrate_task(req->task, cpu, req->dest_cpu);
 		local_irq_enable();
-
-		complete(&req->done);
+		if (!migrated) {
+			/*
+			 * If the process has not been migrated, let it run
+			 * until it reaches a migration_check() so it can
+			 * wake us up.
+			 */
+			spin_lock_irq(&rq->lock);
+			head = &rq->migration_queue;
+			list_add(&req->list, head);
+			if (req->task->se.on_rq
+					|| !task_migrate_count(req->task)) {
+				/*

kernel/sched.c static int migration_thread(void *data) · line 4974

Quoted 10 lines

kernel/sched.c +10 -0

+				 * The process is on the runqueue, it could
+				 * exit its critical section at any moment,
+				 * don't race with it and retry actively.
+				 * Also, if the thread is not on the runqueue
+				 * and has a zero migration count
+				 * (__migrate_task failed because cpus allowed
+				 * changed), just retry.
+				 */
+				spin_unlock_irq(&rq->lock);
+				continue;

Again, this can deadlock. migration_thread() is SCHED_FIFO, and it shares the same CPU with req->task. We are doing a busy-wait loop, req->task may have no chance to finish its critical section.

kernel/sched.c static int migration_thread(void *data) · line 4984

Quoted 10 lines

kernel/sched.c +10 -0

+			}
+			set_tsk_thread_flag(req->task, TIF_NEED_MIGRATE);
+			set_current_state(TASK_INTERRUPTIBLE);
+			spin_unlock_irq(&rq->lock);
+			/*
+			 * Wait for the process currently in its critical
+			 * section.
+			 */
+			wake_up_process(req->task);
+			schedule();

As Peter pointed out, we hold up all other migration requests.

And worse, this can hang forever (until another req comes). do_check_migrate() can wake_up() the wrong rq.

set_current_state(TASK_INTERRUPTIBLE) is bogus, we can miss a wakeup from (say) sched_migrate_task().

Oleg.

Mathieu Desnoyers

2007-07-14 20:33 UTC #14 lore raw

Re: [RFC] Thread Migration Preemption - v4

Quoted 29 lines · * Oleg Nesterov ([email protected]) wrote:

Quoted 28 lines · Mathieu Desnoyers

kernel/sched.c +19 -3

@@ -4891,10 +4948,42 @@ static int migration_thread(void *data)
 		list_del_init(head->next);
 
 		spin_unlock(&rq->lock);
-		__migrate_task(req->task, cpu, req->dest_cpu);
+		migrated = __migrate_task(req->task, cpu, req->dest_cpu);
 		local_irq_enable();
-
-		complete(&req->done);
+		if (!migrated) {
+			/*
+			 * If the process has not been migrated, let it run
+			 * until it reaches a migration_check() so it can
+			 * wake us up.
+			 */
+			spin_lock_irq(&rq->lock);
+			head = &rq->migration_queue;
+			list_add(&req->list, head);
+			if (req->task->se.on_rq
+					|| !task_migrate_count(req->task)) {
+				/*
+				 * The process is on the runqueue, it could
+				 * exit its critical section at any moment,
+				 * don't race with it and retry actively.
+				 * Also, if the thread is not on the runqueue
+				 * and has a zero migration count
+				 * (__migrate_task failed because cpus allowed

Quoted 9 lines

kernel/sched.c static int migration_thread(void *data) · line 4974
Quoted 4 lines
kernel/sched.c +4 -0
+				 * changed), just retry.
+				 */
+				spin_unlock_irq(&rq->lock);
+				continue;
Again, this can deadlock. migration_thread() is SCHED_FIFO, and it shares the same CPU with req->task. We are doing a busy-wait loop, req->task may have no chance to finish its critical section.

If we share the CPU with the other thread, it means that it won't be on the runqueue while we are holding the rq lock. This first case will then end up in the else branch.

The other case, !task_migrate_count(req->task), is meant to check if the process has been scheduled between the unlock/lock of the rq. In this case, it has already decremented its migrate_count to 0.

Quoted 13 lines

kernel/sched.c static int migration_thread(void *data) · line 4984
Quoted 10 lines
kernel/sched.c +10 -0
+			}
+			set_tsk_thread_flag(req->task, TIF_NEED_MIGRATE);
+			set_current_state(TASK_INTERRUPTIBLE);
+			spin_unlock_irq(&rq->lock);
+			/*
+			 * Wait for the process currently in its critical
+			 * section.
+			 */
+			wake_up_process(req->task);
+			schedule();
As Peter pointed out, we hold up all other migration requests.

Quoted 2 lines

And worse, this can hang forever (until another req comes). do_check_migrate() can wake_up() the wrong rq.

True.

Quoted 4 lines

set_current_state(TASK_INTERRUPTIBLE) is bogus, we can miss a wakeup from (say) sched_migrate_task().

Yep, this is why it's an RFC. We will have to work on this a little more.

Regards,

Mathieu

Quoted 2 lines

Oleg.

Signature · 3 lines

Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

Oleg Nesterov

author

2007-07-14 20:41 UTC #15 lore raw

Re: [RFC] Thread Migration Preemption - v4

Quoted 41 lines · Mathieu Desnoyers

Quoted 29 lines · * Oleg Nesterov ([email protected]) wrote:

Quoted 28 lines · Mathieu Desnoyers

kernel/sched.c +19 -3

@@ -4891,10 +4948,42 @@ static int migration_thread(void *data)
 		list_del_init(head->next);
 
 		spin_unlock(&rq->lock);
-		__migrate_task(req->task, cpu, req->dest_cpu);
+		migrated = __migrate_task(req->task, cpu, req->dest_cpu);
 		local_irq_enable();
-
-		complete(&req->done);
+		if (!migrated) {
+			/*
+			 * If the process has not been migrated, let it run
+			 * until it reaches a migration_check() so it can
+			 * wake us up.
+			 */
+			spin_lock_irq(&rq->lock);
+			head = &rq->migration_queue;
+			list_add(&req->list, head);
+			if (req->task->se.on_rq
+					|| !task_migrate_count(req->task)) {
+				/*
+				 * The process is on the runqueue, it could
+				 * exit its critical section at any moment,
+				 * don't race with it and retry actively.
+				 * Also, if the thread is not on the runqueue
+				 * and has a zero migration count
+				 * (__migrate_task failed because cpus allowed

Quoted 9 lines

kernel/sched.c static int migration_thread(void *data) · line 4974
Quoted 4 lines
kernel/sched.c +4 -0
+				 * changed), just retry.
+				 */
+				spin_unlock_irq(&rq->lock);
+				continue;
Again, this can deadlock. migration_thread() is SCHED_FIFO, and it shares the same CPU with req->task. We are doing a busy-wait loop, req->task may have no chance to finish its critical section.

Quoted 2 lines

If we share the CPU with the other thread, it means that it won't be on the runqueue while we are holding the rq lock.

Why? The req->task could be runnable, but preempted by migration_thread(). In that case req->task->se.on_rq should be true.

I didn't read the new scheduler yet, but I belive on_rq == 0 only when the task sleeps, it is like the current ->array = NULL. Please correct me if I am wrong.

Oleg.