[PATCH 02/13] sched/fair: Robustify CFS-bandwidth timer locking

[Tom Zanussi <zanussi@kernel.org>]

4.14.109-rt58-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Peter Zijlstra <peterz@infradead.org>

[ Upstream commit a44c9da61ad3334a9563102e0194d7197b222ec2 ]

Traditionally hrtimer callbacks were run with IRQs disabled, but with
the introduction of HRTIMER_MODE_SOFT it is possible they run from
SoftIRQ context, which does _NOT_ have IRQs disabled.

Allow for the CFS bandwidth timers (period_timer and slack_timer) to
be ran from SoftIRQ context; this entails removing the assumption that
IRQs are already disabled from the locking.

While mainline doesn't strictly need this, -RT forces all timers not
explicitly marked with MODE_HARD into MODE_SOFT and trips over this.
And marking these timers as MODE_HARD doesn't make sense as they're
not required for RT operation and can potentially be quite expensive.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reported-by: Tom Putzeys <tom.putzeys@be.atlascopco.com>
Tested-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20190107125231.GE14122@hirez.programming.kicks-ass.net
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
---
 kernel/sched/fair.c | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9e6ca7d463c0..46403e462404 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4378,7 +4378,7 @@ static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b,
 		struct rq *rq = rq_of(cfs_rq);
 		struct rq_flags rf;
 
-		rq_lock(rq, &rf);
+		rq_lock_irqsave(rq, &rf);
 		if (!cfs_rq_throttled(cfs_rq))
 			goto next;
 
@@ -4395,7 +4395,7 @@ static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b,
 			unthrottle_cfs_rq(cfs_rq);
 
 next:
-		rq_unlock(rq, &rf);
+		rq_unlock_irqrestore(rq, &rf);
 
 		if (!remaining)
 			break;
@@ -4411,7 +4411,7 @@ static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b,
  * period the timer is deactivated until scheduling resumes; cfs_b->idle is
  * used to track this state.
  */
-static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
+static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun, unsigned long flags)
 {
 	u64 runtime, runtime_expires;
 	int throttled;
@@ -4453,11 +4453,11 @@ static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
 	while (throttled && cfs_b->runtime > 0 && !cfs_b->distribute_running) {
 		runtime = cfs_b->runtime;
 		cfs_b->distribute_running = 1;
-		raw_spin_unlock(&cfs_b->lock);
+		raw_spin_unlock_irqrestore(&cfs_b->lock, flags);
 		/* we can't nest cfs_b->lock while distributing bandwidth */
 		runtime = distribute_cfs_runtime(cfs_b, runtime,
 						 runtime_expires);
-		raw_spin_lock(&cfs_b->lock);
+		raw_spin_lock_irqsave(&cfs_b->lock, flags);
 
 		cfs_b->distribute_running = 0;
 		throttled = !list_empty(&cfs_b->throttled_cfs_rq);
@@ -4566,17 +4566,18 @@ static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq)
 static void do_sched_cfs_slack_timer(struct cfs_bandwidth *cfs_b)
 {
 	u64 runtime = 0, slice = sched_cfs_bandwidth_slice();
+	unsigned long flags;
 	u64 expires;
 
 	/* confirm we're still not at a refresh boundary */
-	raw_spin_lock(&cfs_b->lock);
+	raw_spin_lock_irqsave(&cfs_b->lock, flags);
 	if (cfs_b->distribute_running) {
-		raw_spin_unlock(&cfs_b->lock);
+		raw_spin_unlock_irqrestore(&cfs_b->lock, flags);
 		return;
 	}
 
 	if (runtime_refresh_within(cfs_b, min_bandwidth_expiration)) {
-		raw_spin_unlock(&cfs_b->lock);
+		raw_spin_unlock_irqrestore(&cfs_b->lock, flags);
 		return;
 	}
 
@@ -4587,18 +4588,18 @@ static void do_sched_cfs_slack_timer(struct cfs_bandwidth *cfs_b)
 	if (runtime)
 		cfs_b->distribute_running = 1;
 
-	raw_spin_unlock(&cfs_b->lock);
+	raw_spin_unlock_irqrestore(&cfs_b->lock, flags);
 
 	if (!runtime)
 		return;
 
 	runtime = distribute_cfs_runtime(cfs_b, runtime, expires);
 
-	raw_spin_lock(&cfs_b->lock);
+	raw_spin_lock_irqsave(&cfs_b->lock, flags);
 	if (expires == cfs_b->runtime_expires)
 		cfs_b->runtime -= min(runtime, cfs_b->runtime);
 	cfs_b->distribute_running = 0;
-	raw_spin_unlock(&cfs_b->lock);
+	raw_spin_unlock_irqrestore(&cfs_b->lock, flags);
 }
 
 /*
@@ -4676,20 +4677,21 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
 {
 	struct cfs_bandwidth *cfs_b =
 		container_of(timer, struct cfs_bandwidth, period_timer);
+	unsigned long flags;
 	int overrun;
 	int idle = 0;
 
-	raw_spin_lock(&cfs_b->lock);
+	raw_spin_lock_irqsave(&cfs_b->lock, flags);
 	for (;;) {
 		overrun = hrtimer_forward_now(timer, cfs_b->period);
 		if (!overrun)
 			break;
 
-		idle = do_sched_cfs_period_timer(cfs_b, overrun);
+		idle = do_sched_cfs_period_timer(cfs_b, overrun, flags);
 	}
 	if (idle)
 		cfs_b->period_active = 0;
-	raw_spin_unlock(&cfs_b->lock);
+	raw_spin_unlock_irqrestore(&cfs_b->lock, flags);
 
 	return idle ? HRTIMER_NORESTART : HRTIMER_RESTART;
 }
-- 
2.14.1