From: "Ahmed S. Darwish" a.darwish@linutronix.de
[ Upstream commit 2c8bd58812ee3dbf0d78b566822f7eacd34bdd7b ]
To minimize latency, PREEMPT_RT kernels expires hrtimers in preemptible softirq context by default. This can be overriden by marking the timer's expiry with HRTIMER_MODE_HARD.
sched_clock_timer is missing this annotation: if its callback is preempted and the duration of the preemption exceeds the wrap around time of the underlying clocksource, sched clock will get out of sync.
Mark the sched_clock_timer for expiry in hard interrupt context.
Signed-off-by: Ahmed S. Darwish a.darwish@linutronix.de Signed-off-by: Thomas Gleixner tglx@linutronix.de Link: https://lkml.kernel.org/r/20200309181529.26558-1-a.darwish@linutronix.de Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/time/sched_clock.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c index e4332e3e2d569..fa3f800d7d763 100644 --- a/kernel/time/sched_clock.c +++ b/kernel/time/sched_clock.c @@ -208,7 +208,8 @@ sched_clock_register(u64 (*read)(void), int bits, unsigned long rate)
if (sched_clock_timer.function != NULL) { /* update timeout for clock wrap */ - hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL); + hrtimer_start(&sched_clock_timer, cd.wrap_kt, + HRTIMER_MODE_REL_HARD); }
r = rate; @@ -254,9 +255,9 @@ void __init generic_sched_clock_init(void) * Start the timer to keep sched_clock() properly updated and * sets the initial epoch. */ - hrtimer_init(&sched_clock_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); + hrtimer_init(&sched_clock_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD); sched_clock_timer.function = sched_clock_poll; - hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL); + hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL_HARD); }
/* @@ -293,7 +294,7 @@ void sched_clock_resume(void) struct clock_read_data *rd = &cd.read_data[0];
rd->epoch_cyc = cd.actual_read_sched_clock(); - hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL); + hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL_HARD); rd->read_sched_clock = cd.actual_read_sched_clock; }