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: Srivatsa Vaddagiri <vatsa@codeaurora.org>
Change-Id: I11a13be1d9db3a749614ccf3d4f5fb7bf6f18fa1
(cherry picked from commit 4ca1d04ea0bdc225cc7db302172f3375a63f44de)

kernel/sched/core.c

@@ -401,9 +401,16 @@ 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);
 }
@@ -421,7 +428,8 @@ 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;