x86: reimplement ___preempt_schedule*() using THUNK helpers

Peter, Ingo, please consider for inclusion.

Changes:

v3: added the acks from Andy, otherwise unchanged

v2: fix the naming in thunk_32.S (thanks Denys!)

And it seems that the patch below (on top of 1/2) also makes sense...

Oleg.

 arch/x86/kernel/Makefile  |    2 --
 arch/x86/kernel/preempt.S |   25 -------------------------
 arch/x86/lib/Makefile     |    2 +-
 arch/x86/lib/thunk_32.S   |   20 ++++++++++++++++----
 arch/x86/lib/thunk_64.S   |    7 +++++++
 5 files changed, 24 insertions(+), 32 deletions(-)

@@ -166,8 +166,9 @@ static inline int arch_irqs_disabled(voi
 
 #else
 
-#ifdef CONFIG_X86_64
 #define ARCH_LOCKDEP_SYS_EXIT		call lockdep_sys_exit_thunk
+
+#ifdef CONFIG_X86_64
 #define ARCH_LOCKDEP_SYS_EXIT_IRQ	\
 	TRACE_IRQS_ON; \
 	sti; \

@@ -176,17 +177,7 @@ static inline int arch_irqs_disabled(voi
 	RESTORE_REST; \
 	cli; \
 	TRACE_IRQS_OFF;
-
 #else
-#define ARCH_LOCKDEP_SYS_EXIT			\
-	pushl %eax;				\
-	pushl %ecx;				\
-	pushl %edx;				\
-	call lockdep_sys_exit;			\
-	popl %edx;				\
-	popl %ecx;				\
-	popl %eax;
-
 #define ARCH_LOCKDEP_SYS_EXIT_IRQ
 #endif
 

@@ -33,6 +33,10 @@
 	THUNK trace_hardirqs_off_thunk,trace_hardirqs_off_caller,1
 #endif
 
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	THUNK lockdep_sys_exit_thunk,lockdep_sys_exit
+#endif
+
 #ifdef CONFIG_PREEMPT
 	THUNK ___preempt_schedule, preempt_schedule
 #ifdef CONFIG_CONTEXT_TRACKING

___preempt_schedule() does SAVE_ALL/RESTORE_ALL but this is suboptimal, we do not need to save/restore the callee-saved register. And we already have arch/x86/lib/thunk_*.S which implements the similar asm wrappers, so it makes sense to redefine ___preempt_schedule() as "THUNK ..." and remove preempt.S altogether.

---
 arch/x86/kernel/Makefile  |    2 --
 arch/x86/kernel/preempt.S |   25 -------------------------
 arch/x86/lib/thunk_32.S   |   20 ++++++++++++++++----
 arch/x86/lib/thunk_64.S   |    7 +++++++
 4 files changed, 23 insertions(+), 31 deletions(-)
 delete mode 100644 arch/x86/kernel/preempt.S

index b5ea75c..58cf60b 100644
@@ -39,8 +39,6 @@ obj-y			+= tsc.o tsc_msr.o io_delay.o rtc.o
 obj-y			+= pci-iommu_table.o
 obj-y			+= resource.o
 
-obj-$(CONFIG_PREEMPT)	+= preempt.o
-
 obj-y				+= process.o
 obj-y				+= i387.o xsave.o
 obj-y				+= ptrace.o

deleted file mode 100644
index ca7f0d5..0000000
@@ -1,25 +0,0 @@
-
-#include <linux/linkage.h>
-#include <asm/dwarf2.h>
-#include <asm/asm.h>
-#include <asm/calling.h>
-
-ENTRY(___preempt_schedule)
-	CFI_STARTPROC
-	SAVE_ALL
-	call preempt_schedule
-	RESTORE_ALL
-	ret
-	CFI_ENDPROC
-
-#ifdef CONFIG_CONTEXT_TRACKING
-
-ENTRY(___preempt_schedule_context)
-	CFI_STARTPROC
-	SAVE_ALL
-	call preempt_schedule_context
-	RESTORE_ALL
-	ret
-	CFI_ENDPROC
-
-#endif

index 28f85c9..e9acf5f 100644
@@ -7,16 +7,19 @@
 	#include <linux/linkage.h>
 	#include <asm/asm.h>
 
-#ifdef CONFIG_TRACE_IRQFLAGS
 	/* put return address in eax (arg1) */
-	.macro thunk_ra name,func
+	.macro THUNK name, func, put_ret_addr_in_eax=0
 	.globl \name
 \name:
 	pushl %eax
 	pushl %ecx
 	pushl %edx
+
+	.if \put_ret_addr_in_eax
 	/* Place EIP in the arg1 */
 	movl 3*4(%esp), %eax
+	.endif
+
 	call \func
 	popl %edx
 	popl %ecx

@@ -25,6 +28,15 @@
 	_ASM_NOKPROBE(\name)
 	.endm
 
-	thunk_ra trace_hardirqs_on_thunk,trace_hardirqs_on_caller
-	thunk_ra trace_hardirqs_off_thunk,trace_hardirqs_off_caller
+#ifdef CONFIG_TRACE_IRQFLAGS
+	THUNK trace_hardirqs_on_thunk,trace_hardirqs_on_caller,1
+	THUNK trace_hardirqs_off_thunk,trace_hardirqs_off_caller,1
+#endif
+
+#ifdef CONFIG_PREEMPT
+	THUNK ___preempt_schedule, preempt_schedule
+#ifdef CONFIG_CONTEXT_TRACKING
+	THUNK ___preempt_schedule_context, preempt_schedule_context
 #endif
+#endif
+

index 92d9fea..b30b5eb 100644
@@ -38,6 +38,13 @@
 	THUNK lockdep_sys_exit_thunk,lockdep_sys_exit
 #endif
 
+#ifdef CONFIG_PREEMPT
+	THUNK ___preempt_schedule, preempt_schedule
+#ifdef CONFIG_CONTEXT_TRACKING
+	THUNK ___preempt_schedule_context, preempt_schedule_context
+#endif
+#endif
+
 	/* SAVE_ARGS below is used only for the .cfi directives it contains. */
 	CFI_STARTPROC
 	SAVE_ARGS

1.5.5.1

Trivial. We have "lib-y += thunk_$(BITS).o" at the start, no need to add thunk_64.o if !CONFIG_X86_32.

---
 arch/x86/lib/Makefile |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

index 4d4f96a..66127b9 100644
@@ -39,7 +39,7 @@ endif
 else
         obj-y += iomap_copy_64.o
         lib-y += csum-partial_64.o csum-copy_64.o csum-wrappers_64.o
-        lib-y += thunk_64.o clear_page_64.o copy_page_64.o
+        lib-y += clear_page_64.o copy_page_64.o
         lib-y += memmove_64.o memset_64.o
         lib-y += copy_user_64.o copy_user_nocache_64.o
 	lib-y += cmpxchg16b_emu.o

1.5.5.1

Hi Oleg,

I *think* that this patch is causing the following trace (arch/x86/lib/thunk_64.S:44 is new code introduced by this patch):

[  921.908530] kernel BUG at kernel/sched/core.c:2702!
[  921.909159] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
[  921.910084] Dumping ftrace buffer:
[  921.910626]    (ftrace buffer empty)
[  921.911178] Modules linked in:
[  921.915690] CPU: 18 PID: 9489 Comm: trinity-c195 Not tainted 3.17.0-rc7-next-20141002-sasha-00031-gbdb4244 #1273
[  921.917016] task: ffff8802bd748000 ti: ffff8802bda3c000 task.ti: ffff8802bda3c000
[  921.917752] RIP: __schedule (kernel/sched/core.c:2702 kernel/sched/core.c:2808)
[  921.917752] RSP: 0018:ffff8802bda3c360  EFLAGS: 00010297
[  921.917752] RAX: ffff8802bda3c000 RBX: ffff8808501e2a00 RCX: 0000000000000001
[  921.917752] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000286
[  921.917752] RBP: ffff8802bda3c3c0 R08: 000000000001aa50 R09: 0000000000000000
[  921.917752] R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000012
[  921.917752] R13: ffff8808501e2a00 R14: 0000000000000002 R15: ffff8802bda3c428
[  921.917752] FS:  00007f5475cc2700(0000) GS:ffff880850000000(0000) knlGS:0000000000000000
[  921.917752] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[  921.917752] CR2: 00007f5475abe60c CR3: 00000002bebab000 CR4: 00000000000006a0
[  921.917752] DR0: 00000000006f0000 DR1: 0000000000000000 DR2: 0000000000000000
[  921.917752] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
[  921.917752] Stack:
[  921.917752]  000000000001aa50 ffff8802bd748000 ffff8802bda3ffd8 00000000001e2a00
[  921.917752]  00000000001e2a00 ffff8802bd748000 ffff8802bda3c3a0 00000000001e2a00
[  921.917752]  ffff8802bd748000 000000000001a9ea 0000000000000002 ffff8802bda3c428
[  921.917752] Call Trace:
[  921.917752] schedule_user (kernel/sched/core.c:2894 include/linux/jump_label.h:114 include/linux/context_tracking_state.h:27 include/linux/context_tracking.h:20 kernel/sched/core.c:2909)
[  921.917752] int_careful (arch/x86/kernel/entry_64.S:560)
[  921.917752] ? retint_careful (arch/x86/kernel/entry_64.S:889)
[  921.917752] ? preempt_schedule (./arch/x86/include/asm/preempt.h:80 (discriminator 1) kernel/sched/core.c:2943 (discriminator 1))
[  921.917752] ? preempt_schedule_context (./arch/x86/include/asm/preempt.h:75 kernel/context_tracking.c:143)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  921.917752] ? __schedule (kernel/sched/core.c:2900)
[  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  921.917752] ? ftrace_ops_control_func (kernel/trace/ftrace.c:4780)
[  921.917752] ? ftrace_call (arch/x86/kernel/mcount_64.S:56)
[  921.917752] ? retint_careful (arch/x86/kernel/entry_64.S:886)
[  921.917752] ? __this_cpu_preempt_check (lib/smp_processor_id.c:63)
[  921.917752] ? schedule_user (kernel/sched/core.c:2900)
[  921.917752] ? schedule_user (kernel/sched/core.c:2900)
[  921.917752] ? retint_careful (arch/x86/kernel/entry_64.S:889)
[ 921.917752] Code: 48 c7 c2 50 2d 72 97 be 72 00 00 00 48 c7 c7 eb 26 73 97 c6 05 37 b3 ac 02 01 e8 d4 06 c6 fc e9 0d fb ff ff 0f 1f 80 00 00 00 00 <0f> 0b 66 0f 1f 44 00 00 48 8b 45 c8 48 8b 00 48 83 f8 40 0f 84
All code
========
   0:	48 c7 c2 50 2d 72 97 	mov    $0xffffffff97722d50,%rdx
   7:	be 72 00 00 00       	mov    $0x72,%esi
   c:	48 c7 c7 eb 26 73 97 	mov    $0xffffffff977326eb,%rdi
  13:	c6 05 37 b3 ac 02 01 	movb   $0x1,0x2acb337(%rip)        # 0x2acb351
  1a:	e8 d4 06 c6 fc       	callq  0xfffffffffcc606f3
  1f:	e9 0d fb ff ff       	jmpq   0xfffffffffffffb31
  24:	0f 1f 80 00 00 00 00 	nopl   0x0(%rax)
  2b:*	0f 0b                	ud2    		<-- trapping instruction
  2d:	66 0f 1f 44 00 00    	nopw   0x0(%rax,%rax,1)
  33:	48 8b 45 c8          	mov    -0x38(%rbp),%rax
  37:	48 8b 00             	mov    (%rax),%rax
  3a:	48 83 f8 40          	cmp    $0x40,%rax
  3e:	0f                   	.byte 0xf
  3f:	84 00                	test   %al,(%rax)

Code starting with the faulting instruction
===========================================

   0:	0f 0b                	ud2
   2:	66 0f 1f 44 00 00    	nopw   0x0(%rax,%rax,1)
   8:	48 8b 45 c8          	mov    -0x38(%rbp),%rax
   c:	48 8b 00             	mov    (%rax),%rax
   f:	48 83 f8 40          	cmp    $0x40,%rax
  13:	0f                   	.byte 0xf
  14:	84 00                	test   %al,(%rax)
[  921.917752] RIP __schedule (kernel/sched/core.c:2702 kernel/sched/core.c:2808)
[  921.917752]  RSP <ffff8802bda3c360>
[  922.457643] BUG: unable to handle kernel paging request at fffffffc310ead68
[  922.458855] IP: cpuacct_charge (kernel/sched/cpuacct.c:247)
[  922.467627] PGD 17e23067 PUD 0
[  922.467627] Thread overran stack, or stack corrupted
[  922.467627] Oops: 0000 [#2] PREEMPT SMP DEBUG_PAGEALLOC
[  922.467627] Dumping ftrace buffer:
[  922.467627]    (ftrace buffer empty)
[  922.467627] Modules linked in:
[  922.467627] CPU: 18 PID: 9489 Comm: trinity-c195 Tainted: G      D        3.17.0-rc7-next-20141002-sasha-00031-gbdb4244 #1273
[  922.467627] task: ffff8802bd748000 ti: ffff8802bda3c000 task.ti: ffff8802bda3c000
[  922.467627] RIP: cpuacct_charge (kernel/sched/cpuacct.c:247)
[  922.467627] RSP: 0018:ffff880850003d28  EFLAGS: 00010046
[  922.467627] RAX: 000000000000f128 RBX: 00000000932539cd RCX: ffffffff932539cd
[  922.467627] RDX: ffffffff97ea5500 RSI: 0000000000000000 RDI: 0000000000000086
[  922.467627] RBP: ffff880850003d58 R08: 0000000000000000 R09: 0000000000000001
[  922.467627] R10: 0000000000000000 R11: 0000000000009a86 R12: 00000000128d0aa7
[  922.467627] R13: ffff8802bd748000 R14: ffffffff98afaa40 R15: 0000000000000400
[  922.467627] FS:  00007f5475cc2700(0000) GS:ffff880850000000(0000) knlGS:0000000000000000
[  922.467627] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[  922.467627] CR2: fffffffc310ead68 CR3: 00000002bebab000 CR4: 00000000000006a0
[  922.467627] DR0: 00000000006f0000 DR1: 0000000000000000 DR2: 0000000000000000
[  922.467627] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
[  922.467627] Stack:
[  922.467627]  ffffffff931bdb35 ffffffff931bdb35 ffff8802bd748068 ffff88084f106f90
[  922.467627]  00000000128d0aa7 ffff8802bd748000 ffff880850003d98 ffffffff931a7b86
[  922.467627]  000000000001aa9a ffff8802bd748068 ffff88084f106f90 0000000000000000
[  922.467627] Call Trace:
[  922.467627]  <IRQ>
[  922.467627] ? cpuacct_charge (kernel/sched/cpuacct.c:236)
[  922.467627] ? cpuacct_charge (kernel/sched/cpuacct.c:236)
[  922.467627] update_curr (kernel/sched/stats.h:259 kernel/sched/fair.c:723)
[  922.467627] task_tick_fair (kernel/sched/fair.c:2526 (discriminator 2) kernel/sched/fair.c:7512 (discriminator 2))
[  922.467627] scheduler_tick (kernel/sched/core.c:2564)
[  922.467627] update_process_times (kernel/time/timer.c:1391)
[  922.467627] tick_sched_handle.isra.14 (kernel/time/tick-sched.c:152)
[  922.467627] tick_sched_timer (kernel/time/tick-sched.c:1117)
[  922.467627] __run_hrtimer (kernel/time/hrtimer.c:1218 (discriminator 3))
[  922.467627] ? tick_sched_do_timer (kernel/time/tick-sched.c:1101)
[  922.467627] hrtimer_interrupt (kernel/time/hrtimer.c:1307)
[  922.467627] local_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:921)
[  922.467627] smp_apic_timer_interrupt (./arch/x86/include/asm/apic.h:660 arch/x86/kernel/apic/apic.c:945)
[  922.467627] apic_timer_interrupt (arch/x86/kernel/entry_64.S:999)
[  922.467627]  <EOI>
[  922.467627] ? oops_end (./arch/x86/include/asm/paravirt.h:809 arch/x86/kernel/dumpstack.c:240)
[  922.467627] die (arch/x86/kernel/dumpstack.c:313)
[  922.467627] do_trap (arch/x86/kernel/traps.c:132 arch/x86/kernel/traps.c:178)
[  922.467627] do_error_trap (arch/x86/kernel/traps.c:216 include/linux/jump_label.h:114 include/linux/context_tracking_state.h:27 include/linux/context_tracking.h:45 arch/x86/kernel/traps.c:220)
[  922.467627] ? __schedule (kernel/sched/core.c:2702 kernel/sched/core.c:2808)
[  922.467627] ? error_sti (arch/x86/kernel/entry_64.S:1398)
[  922.467627] ? __this_cpu_preempt_check (lib/smp_processor_id.c:63)
[  922.467627] do_invalid_op (arch/x86/kernel/traps.c:232)
[  922.467627] invalid_op (arch/x86/kernel/entry_64.S:1125)
[  922.467627] ? __schedule (kernel/sched/core.c:2702 kernel/sched/core.c:2808)
[  922.467627] schedule_user (kernel/sched/core.c:2894 include/linux/jump_label.h:114 include/linux/context_tracking_state.h:27 include/linux/context_tracking.h:20 kernel/sched/core.c:2909)
[  922.467627] int_careful (arch/x86/kernel/entry_64.S:560)
[  922.467627] ? retint_careful (arch/x86/kernel/entry_64.S:889)
[  922.467627] ? preempt_schedule (./arch/x86/include/asm/preempt.h:80 (discriminator 1) kernel/sched/core.c:2943 (discriminator 1))
[  922.467627] ? preempt_schedule_context (./arch/x86/include/asm/preempt.h:75 kernel/context_tracking.c:143)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? preempt_schedule_context (kernel/context_tracking.c:145)
[  922.467627] ? __schedule (kernel/sched/core.c:2900)
[  922.467627] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
[  922.467627] ? ftrace_ops_control_func (kernel/trace/ftrace.c:4780)
[  922.467627] ? ftrace_call (arch/x86/kernel/mcount_64.S:56)
[  922.467627] ? retint_careful (arch/x86/kernel/entry_64.S:886)
[  922.467627] ? __this_cpu_preempt_check (lib/smp_processor_id.c:63)
[  922.467627] ? schedule_user (kernel/sched/core.c:2900)
[  922.467627] ? schedule_user (kernel/sched/core.c:2900)
[  922.467627] ? retint_careful (arch/x86/kernel/entry_64.S:889)
[ 922.467627] Code: 00 00 00 4d 8b b5 e8 18 00 00 e8 b5 55 02 00 85 c0 74 09 80 3d e4 1c e7 05 00 74 68 49 8b 56 60 48 63 cb 90 48 8b 82 e0 00 00 00 <48> 03 04 cd 00 df e4 97 4c 01 20 48 8b 52 48 48 85 d2 75 e5 e8
All code
========
   0:	00 00                	add    %al,(%rax)
   2:	00 4d 8b             	add    %cl,-0x75(%rbp)
   5:	b5 e8                	mov    $0xe8,%ch
   7:	18 00                	sbb    %al,(%rax)
   9:	00 e8                	add    %ch,%al
   b:	b5 55                	mov    $0x55,%ch
   d:	02 00                	add    (%rax),%al
   f:	85 c0                	test   %eax,%eax
  11:	74 09                	je     0x1c
  13:	80 3d e4 1c e7 05 00 	cmpb   $0x0,0x5e71ce4(%rip)        # 0x5e71cfe
  1a:	74 68                	je     0x84
  1c:	49 8b 56 60          	mov    0x60(%r14),%rdx
  20:	48 63 cb             	movslq %ebx,%rcx
  23:	90                   	nop
  24:	48 8b 82 e0 00 00 00 	mov    0xe0(%rdx),%rax
  2b:*	48 03 04 cd 00 df e4 	add    -0x681b2100(,%rcx,8),%rax		<-- trapping instruction
  32:	97
  33:	4c 01 20             	add    %r12,(%rax)
  36:	48 8b 52 48          	mov    0x48(%rdx),%rdx
  3a:	48 85 d2             	test   %rdx,%rdx
  3d:	75 e5                	jne    0x24
  3f:	e8                   	.byte 0xe8
	...

Code starting with the faulting instruction
===========================================
0: 48 03 04 cd 00 df e4 add -0x681b2100(,%rcx,8),%rax
7: 97

   8:	4c 01 20             	add    %r12,(%rax)
   b:	48 8b 52 48          	mov    0x48(%rdx),%rdx
   f:	48 85 d2             	test   %rdx,%rdx
  12:	75 e5                	jne    0xfffffffffffffff9
  14:	e8                   	.byte 0xe8
	...
[  922.467627] RIP cpuacct_charge (kernel/sched/cpuacct.c:247)
[  922.467627]  RSP <ffff880850003d28>
[  922.467627] CR2: fffffffc310ead68

Thanks,
Sasha

<snip lots of repeats of this>

I *think* this is because RBP isn't being saved across task switch anymore?

Without CONFIG_FRAME_POINTERS that night not be a problem...

Hi Sasha,

Not sure, but I'm afraid your guess can be correct...

OK, this is schedule_debug() -> BUG_ON(unlikely(task_stack_end_corrupted(prev))) in linux-next.

But at first glance this doesn't match the disassembled code... Could you send me (privately) your kernel/sched/core.c just in case? And .config please. And, if possible, kernel/sched/core.s

Oleg.

Is this thing missing a flags or cc clobber:

# define __preempt_schedule() asm ("call ___preempt_schedule")

Also, I'm at a loss as to wtf all this code is doing.

There's preempt_schedule, which appears to be a normal C function.

There's ___preempt_schedule, which is written in assembly and calls preempt_schedule.

Then there's __preempt_schedule, which is an inline assembler function that calls ___preempt_schedule.

Is this all just to make the call sequence for preempt_schedule shorter?

--Andy

Andy Lutomirski
AMA Capital Management, LLC

SAVE_ARGS/RESTORE_ARGS, which is what THUNK uses, doesn't push/pop %rbp

Before, SAVE_ALL/RESTORE_ALL were being used around the call to preempt_schedule(). So from the symptoms I thought this was the problem.

rbp is callee-saved no matter what, unless my memory of the ABI is *waaaaay* off.

--Andy

Yes, it is.

Sent from my mobile phone.  Please pardon brevity and lack of formatting.

So far I still do not think (at least I do not understand how) this patch could introduce the problem. I can be wrong of course...

Let's look at this trace again,

OK, let's assume this is BUG_ON(unlikely(task_stack_end_corrupted(prev))) in schedule_debug().

...

...

A lOT of repeats of above, so we can run out of stack and in this case task_stack_end_corrupted() is clear.

And I _think_ that preempt_schedule_context() should be fixed anyway, although I am not sure there is no something else. It does:

	preempt_disable_notrace();
	prev_ctx = exception_enter();
	preempt_enable_no_resched_notrace();

	preempt_schedule();

	preempt_disable_notrace();
	exception_exit(prev_ctx);
	preempt_enable_notrace();

but exception_exit() is heavy, it is quite possible that TIF_NEED_RESCHED and thus set_preempt_need_resched() can be set again when we call preempt_enable_notrace(). And in this case preempt_schedule_context() will be called recursively.

Frederic, how about the patch below?

In _theory_ this can explain this OOPS unless I am totally confused.

Oleg.

@@ -134,15 +134,17 @@ asmlinkage __visible void __sched notrac
 	 * and the tracer calls preempt_enable_notrace() causing
 	 * an infinite recursion.
 	 */
-	preempt_disable_notrace();
-	prev_ctx = exception_enter();
-	preempt_enable_no_resched_notrace();
-
-	preempt_schedule();
-
-	preempt_disable_notrace();
-	exception_exit(prev_ctx);
-	preempt_enable_notrace();
+	do {
+		preempt_disable_notrace();
+		prev_ctx = exception_enter();
+		preempt_enable_no_resched_notrace();
+
+		preempt_schedule();
+
+		preempt_disable_notrace();
+		exception_exit(prev_ctx);
+		preempt_enable_no_resched_notrace();
+	} while (need_resched());
 }
 EXPORT_SYMBOL_GPL(preempt_schedule_context);
 #endif /* CONFIG_PREEMPT */

Ah, thanks, now I understand what you meant. I thought you meant switch_to().

Yes, I thought about this difference too, but so far I fail to understand how this can make a difference, according to calling.h it is callee-saved.

Oleg.

Yes, it should probably have a cc clobber. Although I think thet gcc actually assumes all asms clobber flags on x86, so it shouldn't matter.

Not so much the call sequence, but the code around the call - not havign to spill live registers etc. But yes.

Linus

Well, calling.h says "rflags is clobbered", so probably yes?

Yes, please look at 1a338ac32ca630f67df25b4a16436cccc314e997

sched, x86: Optimize the preempt_schedule() call

Remove the bloat of the C calling convention out of the preempt_enable() sites by creating an ASM wrapper which allows us to do an asm("call ___preempt_schedule") instead.

Oleg.

Why the hell is it using "preempt_enable_notrace()" in the first place? Shouldn't it use "preempt_enable_no_resched_notrace()", since we do *not* want it to schedule, since the whole *point* is that any scheduling should be called within "exception" context.

Why do it multiple times? The whole concept is fundamentally racy anyway, in it doesn't guarantee that any *new* "need_resched()" would be reacted to (since they could happen *after* the test), so there's no point in trying to fix the "race", since it always remains at the last iteration anyway. So adding the loop looks like just voodoo programming, not actually fixing anything.

The real fix would appear to be to use "preempt_enable_no_resched_notrace()", which your patch did, but without the loop.

Yes?

Linus

Actually, the real fix would be to not be stupid, and just make the code do something like

and *not* enable preemption around the scheduling at all. The whole enable and then re-disable seems entirely broken, and comes from the code using "preempt_schedule()" which doesn't work while preemption is disabled. So don't do that then.

No?

Linus

Could you please spell?

I don't even understand "RBP isn't being saved", SAVE_CONTEXT/RESTORE_CONTEXT do push/pop %rbp?

Thanks,

Oleg.

Yes, this this is the main problem.

But in this case we rely on scheduler_ipi() and return-from-irq path?

Not sure... preempt_schedule() does the same and afaics for good reason.

But perhaps you are right. I am already sleeping, will try to recheck tomorrow. And in fact I got lost in preempt.h files... I can't even understand why __preempt_schedule_context() is only called by preempt_enable_notrace().

Oleg.

Again, it is too late for me... Most probably I am wrong, but somehow it seems to me that the real fix should try to kill preempt_schedule_context() altogether and teach preempt_schedule() to play well with CONTEXT_TRACKING.

Oleg.

Yes, I think you are right. And I hate to admit that I didn't think about this simplification. The only complication is that we should move this function from context_tracking.c to sched/core.c.

However, I still think we need the need_resched() loop, we can't do this only once.

And in fact the simplest fix could just turn it into

	local_irq_disable();
	preempt_schedule_irq();
	local_irq_enable();

Yes, the very fact that

	preempt_enable() != trace_preempt_on() + preempt_enable_notrace()

looks simply wrong imo. And preempt_enable_notrace() has users outside of the tracing code which can run in IN_USER state. For example, why should __perf_sw_event() worry about context_tracking.state?

OTOH, if the caller of preempt_enable_notrace() actually needs to take care of potential IN_USER state, then it probably has other problems. And indeed, ftrace_ops_control_func() has to check rcu_is_watching() anyway.

IOW, imho 29bb9e5a75 "tracing/context-tracking: Add preempt_schedule_context() for tracing" was not a right solution. Perhaps the tracing functions can be changed to switch to IN_KERNEL mode, or at least perhaps we can add the special preempt_disable_ftrace() helper. But this needs another discussion.

Either way, I do think that preempt_schedule_context() in its current form must die.

Oleg.

preempt_schedule_context() does preempt_enable_notrace() at the end and this can call the same function again; exception_exit() is heavy and it is quite possible that need-resched is true again.

1. Change this code to dec preempt_count() and check need_resched() by hand.

2. As Linus suggested, we can use the PREEMPT_ACTIVE bit and avoid the enable/disable dance around __schedule(). But in this case we need to move into sched/core.c.

3. Cosmetic, but x86 forgets to declare this function. This doesn't really matter because it is only called by asm helpers, still it make sense to add the declaration into asm/preempt.h to match preempt_schedule().

---
 arch/x86/include/asm/preempt.h |    1 +
 kernel/context_tracking.c      |   40 ---------------------------------------
 kernel/sched/core.c            |   41 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 42 insertions(+), 40 deletions(-)

index 7024c12..4008734 100644
@@ -105,6 +105,7 @@ static __always_inline bool should_resched(void)
 # ifdef CONFIG_CONTEXT_TRACKING
     extern asmlinkage void ___preempt_schedule_context(void);
 #   define __preempt_schedule_context() asm ("call ___preempt_schedule_context")
+    extern asmlinkage void preempt_schedule_context(void);
 # endif
 #endif
 

index 5664985..937ecdf 100644
@@ -107,46 +107,6 @@ void context_tracking_user_enter(void)
 }
 NOKPROBE_SYMBOL(context_tracking_user_enter);
 
-#ifdef CONFIG_PREEMPT
-/**
- * preempt_schedule_context - preempt_schedule called by tracing
- *
- * The tracing infrastructure uses preempt_enable_notrace to prevent
- * recursion and tracing preempt enabling caused by the tracing
- * infrastructure itself. But as tracing can happen in areas coming
- * from userspace or just about to enter userspace, a preempt enable
- * can occur before user_exit() is called. This will cause the scheduler
- * to be called when the system is still in usermode.
- *
- * To prevent this, the preempt_enable_notrace will use this function
- * instead of preempt_schedule() to exit user context if needed before
- * calling the scheduler.
- */
-asmlinkage __visible void __sched notrace preempt_schedule_context(void)
-{
-	enum ctx_state prev_ctx;
-
-	if (likely(!preemptible()))
-		return;
-
-	/*
-	 * Need to disable preemption in case user_exit() is traced
-	 * and the tracer calls preempt_enable_notrace() causing
-	 * an infinite recursion.
-	 */
-	preempt_disable_notrace();
-	prev_ctx = exception_enter();
-	preempt_enable_no_resched_notrace();
-
-	preempt_schedule();
-
-	preempt_disable_notrace();
-	exception_exit(prev_ctx);
-	preempt_enable_notrace();
-}
-EXPORT_SYMBOL_GPL(preempt_schedule_context);
-#endif /* CONFIG_PREEMPT */
-
 /**
  * context_tracking_user_exit - Inform the context tracking that the CPU is
  *                              exiting userspace mode and entering the kernel.

1.5.5.1

And, Frederic, this is off-topic but I am just curious...

I can't understand why exception_enter() calls context_tracking_user_exit() unconditionally (unlike exception_exit), and why enter/exit need to check context_tracking.state with irqs disabled.

IOW, any reason why the patch below is wrong?

Of course, context_tracking is per-cpu, so

	if (context_tracking_in_user()) {
		local_irq_save(flags);
		...

can be preempted and change the state on another CPU. But this should be fine because the task must see the same .state on all CPU's or the whole preempt context-tracking logic is broken?

Oleg.

@@ -29,15 +29,14 @@ static inline void user_exit(void)
 
 static inline enum ctx_state exception_enter(void)
 {
-	enum ctx_state prev_ctx;
-
-	if (!context_tracking_is_enabled())
-		return 0;
-
-	prev_ctx = this_cpu_read(context_tracking.state);
-	context_tracking_user_exit();
+	if (context_tracking_is_enabled()) {
+		if (context_tracking_in_user()) {
+			context_tracking_user_exit();
+			return IN_USER;
+		}
+	}
 
-	return prev_ctx;
+	return IN_KERNEL;
 }
 
 static inline void exception_exit(enum ctx_state prev_ctx)

@@ -74,8 +74,8 @@ void context_tracking_user_enter(void)
 	/* Kernel threads aren't supposed to go to userspace */
 	WARN_ON_ONCE(!current->mm);
 
-	local_irq_save(flags);
-	if ( __this_cpu_read(context_tracking.state) != IN_USER) {
+	if (!context_tracking_in_user()) {
+		local_irq_save(flags);
 		if (__this_cpu_read(context_tracking.active)) {
 			trace_user_enter(0);
 			/*

@@ -102,8 +102,8 @@ void context_tracking_user_enter(void)
 		 * is false because we know that CPU is not tickless.
 		 */
 		__this_cpu_write(context_tracking.state, IN_USER);
+		local_irq_restore(flags);
 	}
-	local_irq_restore(flags);
 }
 NOKPROBE_SYMBOL(context_tracking_user_enter);
 

@@ -128,8 +128,8 @@ void context_tracking_user_exit(void)
 	if (in_interrupt())
 		return;
 
-	local_irq_save(flags);
-	if (__this_cpu_read(context_tracking.state) == IN_USER) {
+	if (context_tracking_in_user()) {
+		local_irq_save(flags);
 		if (__this_cpu_read(context_tracking.active)) {
 			/*
 			 * We are going to run code that may use RCU. Inform

@@ -140,8 +140,8 @@ void context_tracking_user_exit(void)
 			trace_user_exit(0);
 		}
 		__this_cpu_write(context_tracking.state, IN_KERNEL);
+		local_irq_restore(flags);
 	}
-	local_irq_restore(flags);
 }
 NOKPROBE_SYMBOL(context_tracking_user_exit);