[PATCH AUTOSEL for 3.18 17/63] timers, sched_clock: Update timeout for clock wrap

[Sasha Levin]

From: David Engraf <david.engraf@xxxxxxxxx>

[ Upstream commit 1b8955bc5ac575009835e371ae55e7f3af2197a9 ]

The scheduler clock framework may not use the correct timeout for the clock
wrap. This happens when a new clock driver calls sched_clock_register()
after the kernel called sched_clock_postinit(). In this case the clock wrap
timeout is too long thus sched_clock_poll() is called too late and the clock
already wrapped.

On my ARM system the scheduler was no longer scheduling any other task than
the idle task because the sched_clock() wrapped.

Signed-off-by: David Engraf <david.engraf@xxxxxxxxx>
Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
---
 kernel/time/sched_clock.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
index 01d2d15aa662..830e214f372c 100644
--- a/kernel/time/sched_clock.c
+++ b/kernel/time/sched_clock.c
@@ -146,6 +146,11 @@ void __init sched_clock_register(u64 (*read)(void), int bits,
 	cd.epoch_ns = ns;
 	raw_write_seqcount_end(&cd.seq);
 
+	if (sched_clock_timer.function != NULL) {
+		/* update timeout for clock wrap */
+		hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
+	}
+
 	r = rate;
 	if (r >= 4000000) {
 		r /= 1000000;
-- 
2.14.1