sched/clock: Fix clear_sched_clock_stable() preempt wobbly

Paul reported a problems with clear_sched_clock_stable(). Since we run
all of __clear_sched_clock_stable() from workqueue context, there's a
preempt problem.

Solve it by only running the static_key_disable() from workqueue.

Reported-by: Paul E. McKenney <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

1 files changed, 12 insertions, 5 deletions

diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
index a08795e21628..fec0f58c8dee 100644
--- a/kernel/sched/clock.c
+++ b/kernel/sched/clock.c
@@ -141,7 +141,14 @@ static void __set_sched_clock_stable(void)
 	tick_dep_clear(TICK_DEP_BIT_CLOCK_UNSTABLE);
 }
 
-static void __clear_sched_clock_stable(struct work_struct *work)
+static void __sched_clock_work(struct work_struct *work)
+{
+	static_branch_disable(&__sched_clock_stable);
+}
+
+static DECLARE_WORK(sched_clock_work, __sched_clock_work);
+
+static void __clear_sched_clock_stable(void)
 {
 	struct sched_clock_data *scd = this_scd();
 
@@ -160,11 +167,11 @@ static void __clear_sched_clock_stable(struct work_struct *work)
 			scd->tick_gtod, gtod_offset,
 			scd->tick_raw,  raw_offset);
 
-	static_branch_disable(&__sched_clock_stable);
 	tick_dep_set(TICK_DEP_BIT_CLOCK_UNSTABLE);
-}
 
-static DECLARE_WORK(sched_clock_work, __clear_sched_clock_stable);
+	if (sched_clock_stable())
+		schedule_work(&sched_clock_work);
+}
 
 void clear_sched_clock_stable(void)
 {
@@ -173,7 +180,7 @@ void clear_sched_clock_stable(void)
 	smp_mb(); /* matches sched_clock_init_late() */
 
 	if (sched_clock_running == 2)
-		schedule_work(&sched_clock_work);
+		__clear_sched_clock_stable();
 }
 
 void sched_clock_init_late(void)