[PATCH AUTOSEL for 4.9 058/219] timers, sched_clock: Update timeout for clock wrap

Sasha Levin
2018-03-03T23:56:36Z

From: David Engraf <david.engraf@sysgo.com>

[ 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@sysgo.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
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 a26036d37a38..382b159d8592 100644
--- a/kernel/time/sched_clock.c
+++ b/kernel/time/sched_clock.c
@@ -205,6 +205,11 @@ sched_clock_register(u64 (*read)(void), int bits, unsigned long rate)

update_clock_read_data(&rd);

+ 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