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Commit 39c8206a authored by Srivatsa Vaddagiri's avatar Srivatsa Vaddagiri Committed by Stephen Boyd
Browse files

sched: fix rq->lock recursion 



Enabling SCHED_HRTICK currently results in rq->lock recursion and a hard
hang at bootup.  Essentially try_to_wakeup() grabs rq->lock and tries
arming a hrtimer via hrtimer_restart(), which deep down tries waking up
ksoftirqd, which leads to a recursive call to try_to_wakeup() and thus
attempt to take rq->lock recursively!!

This is fixed by having scheduler queue hrtimer via
__hrtimer_start_range_ns() which avoids waking up ksoftirqd.

Signed-off-by: default avatarSrivatsa Vaddagiri <vatsa@codeaurora.org>
Change-Id: I11a13be1d9db3a749614ccf3d4f5fb7bf6f18fa1
(cherry picked from commit 4ca1d04ea0bdc225cc7db302172f3375a63f44de)
parent 471182d7

kernel/sched/core.c

+10 −2
Original line number Diff line number Diff line
@@ -410,9 +410,16 @@ static enum hrtimer_restart hrtick(struct hrtimer *timer) 
static void __hrtick_start(void *arg)

{

	struct rq *rq = arg;

	struct hrtimer *timer = &rq->hrtick_timer;

	ktime_t soft, hard;

	unsigned long delta;



	soft = hrtimer_get_softexpires(timer);

	hard = hrtimer_get_expires(timer);

	delta = ktime_to_ns(ktime_sub(hard, soft));



	raw_spin_lock(&rq->lock);

	hrtimer_restart(&rq->hrtick_timer);

	__hrtimer_start_range_ns(timer, soft, delta, HRTIMER_MODE_ABS, 0);

	rq->hrtick_csd_pending = 0;

	raw_spin_unlock(&rq->lock);

}
@@ -430,7 +437,8 @@ void hrtick_start(struct rq *rq, u64 delay) 
	hrtimer_set_expires(timer, time);



	if (rq == this_rq()) {

		hrtimer_restart(timer);

		__hrtimer_start_range_ns(timer, ns_to_ktime(delay), 0,

						 HRTIMER_MODE_REL_PINNED, 0);

	} else if (!rq->hrtick_csd_pending) {

		__smp_call_function_single(cpu_of(rq), &rq->hrtick_csd, 0);

		rq->hrtick_csd_pending = 1;