linux-kernel - [PATCH] sched_clock: Avoid corrupting hrtimer tree during suspend

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Date:	Fri, 18 Jul 2014 15:09:52 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: [PATCH] sched_clock: Avoid corrupting hrtimer tree during suspend

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. Fix this
problem by updating the state via update_sched_clock() and
properly restarting the timer via hrtimer_start().

Fixes: a08ca5d1089d "sched_clock: Use an hrtimer instead of timer"
Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
---

I also wonder if we should be restarting the timer during resume
instead of suspend given that the resume path modifies the epoch.
At that point timers can't run because interrupts are disabled and
we don't really care if the timer fires earlier than it's supposed
to anyway because it's just there to avoid rollover events, but
does it seem better to do it that way? I didn't send that version
because this patch is to fix the code intention, but I'm curious
if anyone else feels like it should be changed.

 kernel/time/sched_clock.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
index 445106d2c729..9e32ce88e9ee 100644
--- a/kernel/time/sched_clock.c
+++ b/kernel/time/sched_clock.c
@@ -191,7 +191,9 @@ void __init sched_clock_postinit(void)

 static int sched_clock_suspend(void)
 {
-	sched_clock_poll(&sched_clock_timer);
+	update_sched_clock();
+	/* Restart the timer because we forced an update */
+	hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
 	cd.suspended = true;
 	return 0;
 }
-- 
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