linux-kernel - [GIT PULL] scheduler fixes

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Date:	Wed, 25 May 2016 23:58:24 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [GIT PULL] scheduler fixes

Linus,

Please pull the latest sched-urgent-for-linus git tree from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-urgent-for-linus

   # HEAD: b7e7ade34e6188bee2e3b0d42b51d25137d9e2a5 sched/core: Fix remote wakeups

Two fixes: one for a lost wakeup, the other to fix the compiler optimizing out 
preempt operations on ARM64 (and possibly other non-x86 architectures).

 Thanks,

	Ingo

------------------>
Peter Zijlstra (2):
      sched/preempt: Fix preempt_count manipulations
      sched/core: Fix remote wakeups


 include/asm-generic/preempt.h |  4 ++--
 include/linux/sched.h         |  1 +
 kernel/sched/core.c           | 18 +++++++++++-------
 3 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/include/asm-generic/preempt.h b/include/asm-generic/preempt.h
index 5d8ffa3e6f8c..c1cde3577551 100644
--- a/include/asm-generic/preempt.h
+++ b/include/asm-generic/preempt.h
@@ -7,10 +7,10 @@
 
 static __always_inline int preempt_count(void)
 {
-	return current_thread_info()->preempt_count;
+	return READ_ONCE(current_thread_info()->preempt_count);
 }
 
-static __always_inline int *preempt_count_ptr(void)
+static __always_inline volatile int *preempt_count_ptr(void)
 {
 	return &current_thread_info()->preempt_count;
 }
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 6cc0df970f1a..e053517a88b6 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1533,6 +1533,7 @@ struct task_struct {
 	unsigned sched_reset_on_fork:1;
 	unsigned sched_contributes_to_load:1;
 	unsigned sched_migrated:1;
+	unsigned sched_remote_wakeup:1;
 	unsigned :0; /* force alignment to the next boundary */
 
 	/* unserialized, strictly 'current' */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 404c0784b1fc..7f2cae4620c7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1768,13 +1768,15 @@ void sched_ttwu_pending(void)
 	cookie = lockdep_pin_lock(&rq->lock);
 
 	while (llist) {
+		int wake_flags = 0;
+
 		p = llist_entry(llist, struct task_struct, wake_entry);
 		llist = llist_next(llist);
-		/*
-		 * See ttwu_queue(); we only call ttwu_queue_remote() when
-		 * its a x-cpu wakeup.
-		 */
-		ttwu_do_activate(rq, p, WF_MIGRATED, cookie);
+
+		if (p->sched_remote_wakeup)
+			wake_flags = WF_MIGRATED;
+
+		ttwu_do_activate(rq, p, wake_flags, cookie);
 	}
 
 	lockdep_unpin_lock(&rq->lock, cookie);
@@ -1819,10 +1821,12 @@ void scheduler_ipi(void)
 	irq_exit();
 }
 
-static void ttwu_queue_remote(struct task_struct *p, int cpu)
+static void ttwu_queue_remote(struct task_struct *p, int cpu, int wake_flags)
 {
 	struct rq *rq = cpu_rq(cpu);
 
+	p->sched_remote_wakeup = !!(wake_flags & WF_MIGRATED);
+
 	if (llist_add(&p->wake_entry, &cpu_rq(cpu)->wake_list)) {
 		if (!set_nr_if_polling(rq->idle))
 			smp_send_reschedule(cpu);
@@ -1869,7 +1873,7 @@ static void ttwu_queue(struct task_struct *p, int cpu, int wake_flags)
 #if defined(CONFIG_SMP)
 	if (sched_feat(TTWU_QUEUE) && !cpus_share_cache(smp_processor_id(), cpu)) {
 		sched_clock_cpu(cpu); /* sync clocks x-cpu */
-		ttwu_queue_remote(p, cpu);
+		ttwu_queue_remote(p, cpu, wake_flags);
 		return;
 	}
 #endif