sched_clock: Avoid corrupting hrtimer tree during suspend

bebarino · KAGA-KOKO · commit f723aa1817dd · 2014-07-24T12:02:49.000+02:00
During suspend we call sched_clock_poll() to update the epoch and accumulated time and reprogram the sched_clock_timer to fire before the next wrap-around time. Unfortunately, sched_clock_poll() doesn't restart the timer, instead it relies on the hrtimer layer to do that and during suspend we aren't calling that function from the hrtimer layer. Instead, we're reprogramming the expires time while the hrtimer is enqueued, which can cause the hrtimer tree to be corrupted. Furthermore, we restart the timer during suspend but we update the epoch during resume which seems counter-intuitive. Let's fix this by saving the accumulated state and canceling the timer during suspend. On resume we can update the epoch and restart the timer similar to what we would do if we were starting the clock for the first time. Fixes: a08ca5d "sched_clock: Use an hrtimer instead of timer" Signed-off-by: Stephen Boyd <sboyd@codeaurora.org> Signed-off-by: John Stultz <john.stultz@linaro.org> Link: http://lkml.kernel.org/r/1406174630-23458-1-git-send-email-john.stultz@linaro.org Cc: Ingo Molnar <mingo@kernel.org> Cc: stable <stable@vger.kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
@@ -191,14 +191,16 @@ void __init sched_clock_postinit(void)
 
 static int sched_clock_suspend(void)
 {
-	sched_clock_poll(&sched_clock_timer);
+	update_sched_clock();
+	hrtimer_cancel(&sched_clock_timer);
 	cd.suspended = true;
 	return 0;
 }
 
 static void sched_clock_resume(void)
 {
 	cd.epoch_cyc = read_sched_clock();
+	hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
 	cd.suspended = false;
 }
 

Original file line number	Diff line number	Diff line change
`@@ -191,14 +191,16 @@ void __init sched_clock_postinit(void)`
`191`	`191`
`192`	`192`	`static int sched_clock_suspend(void)`
`193`	`193`	`{`
`194`		`- sched_clock_poll(&sched_clock_timer);`
	`194`	`+ update_sched_clock();`
	`195`	`+ hrtimer_cancel(&sched_clock_timer);`
`195`	`196`	`cd.suspended = true;`
`196`	`197`	`return 0;`
`197`	`198`	`}`
`198`	`199`
`199`	`200`	`static void sched_clock_resume(void)`
`200`	`201`	`{`
`201`	`202`	`cd.epoch_cyc = read_sched_clock();`
	`203`	`+ hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);`
`202`	`204`	`cd.suspended = false;`
`203`	`205`	`}`
`204`	`206`