Linux 3.4.110-rt139-rc1

Dear RT Folks,

This is the RT stable review cycle of patch 3.4.110-rt139-rc1.

Please scream at me if I messed something up. Please test the patches too.

Note, I'm bringing this tree up to stable patches in 4.1.7-rt8. Then I'll be pulling 4.1-rt into stable, as development is now on 4.4-rt. After that, I'll be pulling the 4.1-rt stable changes into the stable trees.

The -rc release will be uploaded to kernel.org and will be deleted when the final release is out. This is just a review release (or release candidate).

The pre-releases will not be pushed to the git repository, only the final release is.

If all goes well, this patch will be converted to the next main release on 2/29/2016.

Enjoy,

-- Steve

To build 3.4.110-rt139-rc1 directly, the following patches should be applied:

http://www.kernel.org/pub/linux/kernel/v3.x/linux-3.4.tar.xz

http://www.kernel.org/pub/linux/kernel/v3.x/patch-3.4.110.xz

http://www.kernel.org/pub/linux/kernel/projects/rt/3.4/patch-3.4.110-rt139-rc1.patch.xz

You can also build from 3.4.110-rt138 by applying the incremental patch:

http://www.kernel.org/pub/linux/kernel/projects/rt/3.4/incr/patch-3.4.110-rt138-rt139-rc1.patch.xz

Changes from 3.4.110-rt138:

---

Josh Cartwright (1):
net: Make synchronize_rcu_expedited() conditional on !RT_FULL

Peter Zijlstra (1):
sched: Introduce the trace_sched_waking tracepoint

Sebastian Andrzej Siewior (1):
dump stack: don't disable preemption during trace

Steven Rostedt (Red Hat) (2):
rtmutex: Have slowfn of rt_mutex_timed_fastlock() use enum Linux 3.4.110-rt139-rc1

Thomas Gleixner (1):
rtmutex: Handle non enqueued waiters gracefully

[email protected] (1):
rtmutex: Use chainwalking control enum

----

 arch/x86/kernel/dumpstack_64.c    |  8 ++++----
 include/trace/events/sched.h      | 30 +++++++++++++++++++++---------
 kernel/rtmutex.c                  |  6 +++---
 kernel/sched/core.c               |  7 +++++--
 kernel/trace/trace_sched_switch.c |  2 +-
 kernel/trace/trace_sched_wakeup.c |  2 +-
 localversion-rt                   |  2 +-
 net/core/dev.c                    |  2 +-
 8 files changed, 37 insertions(+), 22 deletions(-)

3.4.110-rt139-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Thomas Gleixner <[email protected]>

Yimin debugged that in case of a PI wakeup in progress when rt_mutex_start_proxy_lock() calls task_blocks_on_rt_mutex() the latter returns -EAGAIN and in consequence the remove_waiter() call runs into a BUG_ON() because there is nothing to remove.

Guard it with rt_mutex_has_waiters(). This is a quick fix which is easy to backport. The proper fix is to have a central check in remove_waiter() so we can call it unconditionally.

---
 kernel/rtmutex.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 4cc273b85beb..d353e9191955 100644
@@ -1911,7 +1911,7 @@ int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
 		ret = 0;
 	}
 
-	if (unlikely(ret))
+	if (ret && rt_mutex_has_waiters(lock))
 		remove_waiter(lock, waiter);
 
 	raw_spin_unlock(&lock->wait_lock);

2.7.0

3.4.110-rt139-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: "[email protected]" <[email protected]>

In 8930ed80 (rtmutex: Cleanup deadlock detector debug logic), chainwalking control enums were introduced to limit the deadlock detection logic. One of the calls to task_blocks_on_rt_mutex was missed when converting to use the enums.

---
 kernel/rtmutex.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index d353e9191955..fe0cc8f328c8 100644
@@ -1163,7 +1163,7 @@ static void  noinline __sched rt_spin_lock_slowlock(struct rt_mutex *lock)
 	__set_current_state(TASK_UNINTERRUPTIBLE);
 	pi_unlock(&self->pi_lock);
 
-	ret = task_blocks_on_rt_mutex(lock, &waiter, self, 0);
+	ret = task_blocks_on_rt_mutex(lock, &waiter, self, RT_MUTEX_MIN_CHAINWALK);
 	BUG_ON(ret);
 
 	for (;;) {

2.7.0

3.4.110-rt139-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Sebastian Andrzej Siewior <[email protected]>

I see here large latencies during a stack dump on x86. The preempt_disable() and get_cpu() should forbid moving the task to another CPU during a stack dump and avoiding two stack traces in parallel on the same CPU. However a stack trace from a second CPU may still happen in parallel. Also nesting is allowed so a stack trace happens in process-context and we may have another one from IRQ context. With migrate disable we keep this code preemptible and allow a second backtrace on the same CPU by another task.

---
 arch/x86/kernel/dumpstack_64.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

index e8206060a0a8..bebc49d03531 100644
@@ -114,7 +114,7 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs,
 		unsigned long *stack, unsigned long bp,
 		const struct stacktrace_ops *ops, void *data)
 {
-	const unsigned cpu = get_cpu();
+	const unsigned cpu = get_cpu_light();
 	unsigned long *irq_stack_end =
 		(unsigned long *)per_cpu(irq_stack_ptr, cpu);
 	unsigned used = 0;

@@ -191,7 +191,7 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs,
 	 * This handles the process stack:
 	 */
 	bp = ops->walk_stack(tinfo, stack, bp, ops, data, NULL, &graph);
-	put_cpu();
+	put_cpu_light();
 }
 EXPORT_SYMBOL(dump_trace);
 

@@ -205,7 +205,7 @@ show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
 	int cpu;
 	int i;
 
-	preempt_disable();
+	migrate_disable();
 	cpu = smp_processor_id();
 
 	irq_stack_end	= (unsigned long *)(per_cpu(irq_stack_ptr, cpu));

@@ -238,7 +238,7 @@ show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
 		printk(KERN_CONT " %016lx", *stack++);
 		touch_nmi_watchdog();
 	}
-	preempt_enable();
+	migrate_enable();
 
 	printk(KERN_CONT "\n");
 	show_trace_log_lvl(task, regs, sp, bp, log_lvl);

2.7.0

3.4.110-rt139-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Josh Cartwright <[email protected]>

While the use of synchronize_rcu_expedited() might make synchronize_net() "faster", it does so at significant cost on RT systems, as expediting a grace period forcibly preempts any high-priority RT tasks (via the stop_machine() mechanism).

Without this change, we can observe a latency spike up to 30us with cyclictest by rapidly unplugging/reestablishing an ethernet link.

---
 net/core/dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 46f960a4c83b..4dbd27b16d1f 100644
@@ -6081,7 +6081,7 @@ EXPORT_SYMBOL(free_netdev);
 void synchronize_net(void)
 {
 	might_sleep();
-	if (rtnl_is_locked())
+	if (rtnl_is_locked() && !IS_ENABLED(CONFIG_PREEMPT_RT_FULL))
 		synchronize_rcu_expedited();
 	else
 		synchronize_rcu();

2.7.0

3.4.110-rt139-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Peter Zijlstra <[email protected]>

Upstream commit fbd705a0c6184580d0e2fbcbd47a37b6e5822511

Mathieu reported that since 317f394160e9 ("sched: Move the second half of ttwu() to the remote cpu") trace_sched_wakeup() can happen out of context of the waker.

This is a problem when you want to analyse wakeup paths because it is now very hard to correlate the wakeup event to whoever issued the wakeup.

OTOH trace_sched_wakeup() is issued at the point where we set p->state = TASK_RUNNING, which is right were we hand the task off to the scheduler, so this is an important point when looking at scheduling behaviour, up to here its been the wakeup path everything hereafter is due to scheduler policy.

To bridge this gap, introduce a second tracepoint: trace_sched_waking. It is guaranteed to be called in the waker context.

[ Ported to linux-4.1.y-rt kernel by Mathieu Desnoyers. Resolved
conflict: try_to_wake_up_local() does not exist in -rt kernel. Removed its instrumentation hunk. ]

---
 include/trace/events/sched.h      | 30 +++++++++++++++++++++---------
 kernel/sched/core.c               |  7 +++++--
 kernel/trace/trace_sched_switch.c |  2 +-
 kernel/trace/trace_sched_wakeup.c |  2 +-
 4 files changed, 28 insertions(+), 13 deletions(-)

index ea7a2035456d..0a91a095e3c9 100644
@@ -55,9 +55,9 @@ TRACE_EVENT(sched_kthread_stop_ret,
  */
 DECLARE_EVENT_CLASS(sched_wakeup_template,
 
-	TP_PROTO(struct task_struct *p, int success),
+	TP_PROTO(struct task_struct *p),
 
-	TP_ARGS(p, success),
+	TP_ARGS(p),
 
 	TP_STRUCT__entry(
 		__array(	char,	comm,	TASK_COMM_LEN	)

@@ -71,25 +71,37 @@ DECLARE_EVENT_CLASS(sched_wakeup_template,
 		memcpy(__entry->comm, p->comm, TASK_COMM_LEN);
 		__entry->pid		= p->pid;
 		__entry->prio		= p->prio;
-		__entry->success	= success;
+		__entry->success	= 1; /* rudiment, kill when possible */
 		__entry->target_cpu	= task_cpu(p);
 	),
 
-	TP_printk("comm=%s pid=%d prio=%d success=%d target_cpu=%03d",
+	TP_printk("comm=%s pid=%d prio=%d target_cpu=%03d",
 		  __entry->comm, __entry->pid, __entry->prio,
-		  __entry->success, __entry->target_cpu)
+		  __entry->target_cpu)
 );
 
+ /*
+  * Tracepoint called when waking a task; this tracepoint is guaranteed to be
+  * called from the waking context.
+  */
+DEFINE_EVENT(sched_wakeup_template, sched_waking,
+	     TP_PROTO(struct task_struct *p),
+	     TP_ARGS(p));
+
+ /*
+  * Tracepoint called when the task is actually woken; p->state == TASK_RUNNNG.
+  * It it not always called from the waking context.
+  */
 DEFINE_EVENT(sched_wakeup_template, sched_wakeup,
-	     TP_PROTO(struct task_struct *p, int success),
-	     TP_ARGS(p, success));
+	     TP_PROTO(struct task_struct *p),
+	     TP_ARGS(p));
 
 /*
  * Tracepoint for waking up a new task:
  */
 DEFINE_EVENT(sched_wakeup_template, sched_wakeup_new,
-	     TP_PROTO(struct task_struct *p, int success),
-	     TP_ARGS(p, success));
+	     TP_PROTO(struct task_struct *p),
+	     TP_ARGS(p));
 
 #ifdef CREATE_TRACE_POINTS
 static inline long __trace_sched_switch_state(struct task_struct *p)

index 0916d418dabd..cc4df0131023 100644
@@ -1412,10 +1412,11 @@ static void ttwu_activate(struct rq *rq, struct task_struct *p, int en_flags)
 static void
 ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags)
 {
-	trace_sched_wakeup(p, true);
 	check_preempt_curr(rq, p, wake_flags);
 
 	p->state = TASK_RUNNING;
+	trace_sched_wakeup(p);
+
 #ifdef CONFIG_SMP
 	if (p->sched_class->task_woken)
 		p->sched_class->task_woken(rq, p);

@@ -1608,6 +1609,8 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
 	if (!(wake_flags & WF_LOCK_SLEEPER))
 		p->saved_state = TASK_RUNNING;
 
+	trace_sched_waking(p);
+
 	success = 1; /* we're going to change ->state */
 	cpu = task_cpu(p);
 

@@ -1827,7 +1830,7 @@ void wake_up_new_task(struct task_struct *p)
 	rq = __task_rq_lock(p);
 	activate_task(rq, p, 0);
 	p->on_rq = 1;
-	trace_sched_wakeup_new(p, true);
+	trace_sched_wakeup_new(p);
 	check_preempt_curr(rq, p, WF_FORK);
 #ifdef CONFIG_SMP
 	if (p->sched_class->task_woken)

index 7e62c0a18456..5982146ee863 100644
@@ -108,7 +108,7 @@ tracing_sched_wakeup_trace(struct trace_array *tr,
 }
 
 static void
-probe_sched_wakeup(void *ignore, struct task_struct *wakee, int success)
+probe_sched_wakeup(void *ignore, struct task_struct *wakee)
 {
 	struct trace_array_cpu *data;
 	unsigned long flags;

index 9eadedc9b4a8..60160801b8e8 100644
@@ -414,7 +414,7 @@ static void wakeup_reset(struct trace_array *tr)
 }
 
 static void
-probe_wakeup(void *ignore, struct task_struct *p, int success)
+probe_wakeup(void *ignore, struct task_struct *p)
 {
 	struct trace_array_cpu *data;
 	int cpu = smp_processor_id();

2.7.0

3.4.110-rt139-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: "Steven Rostedt (Red Hat)" <[email protected]>

The backport of commit 8930ed80f970 "rtmutex: Cleanup deadlock detector debug logic" had conflicts, and the conflict resolution changed rt_mutex_timed_fastlock()'s parameter to an enum, but missed changing its slowfn's prototype.

---
 kernel/rtmutex.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index fe0cc8f328c8..c2d0f9c8039f 100644
@@ -1633,7 +1633,7 @@ rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
 			enum rtmutex_chainwalk chwalk,
 			int (*slowfn)(struct rt_mutex *lock, int state,
 				      struct hrtimer_sleeper *timeout,
-				      int detect_deadlock))
+				      enum rtmutex_chainwalk chwalk))
 {
 	if (chwalk == RT_MUTEX_MIN_CHAINWALK &&
 	    likely(rt_mutex_cmpxchg(lock, NULL, current))) {

2.7.0

3.4.110-rt139-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: "Steven Rostedt (Red Hat)" <[email protected]>

---
 localversion-rt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 9f63718d5731..c4234a93d790 100644
@@ -1 +1 @@
--rt138
+-rt139-rc1

2.7.0