From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Thu, 31 Aug 2017 18:19:06 +0200
Subject: kernel/hrtimer: don't wakeup a process while holding the hrtimer base lock
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: ce577cb1bba1e2babc208b6277dbf6ba6a784a84
Patch-mainline: Queued in subsystem maintainer repository
References: SLE12 Realtime Extension

We must not wake any process (and thus acquire the pi->lock) while
holding the hrtimer's base lock. This does not happen usually because
the hrtimer-callback is invoked in IRQ-context and so
raise_softirq_irqoff() does not wakeup a process.
However during CPU-hotplug it might get called from hrtimers_dead_cpu()
which would wakeup the thread immediately.

Reported-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
 kernel/time/hrtimer.c |   15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1391,7 +1391,7 @@ static inline int hrtimer_rt_defer(struc
 
 #endif
 
-static void __hrtimer_run_queues(struct hrtimer_cpu_base *cpu_base, ktime_t now)
+static int __hrtimer_run_queues(struct hrtimer_cpu_base *cpu_base, ktime_t now)
 {
 	struct hrtimer_clock_base *base = cpu_base->clock_base;
 	unsigned int active = cpu_base->active_bases;
@@ -1432,8 +1432,7 @@ static void __hrtimer_run_queues(struct
 				raise = 1;
 		}
 	}
-	if (raise)
-		raise_softirq_irqoff(HRTIMER_SOFTIRQ);
+	return raise;
 }
 
 #ifdef CONFIG_HIGH_RES_TIMERS
@@ -1447,6 +1446,7 @@ void hrtimer_interrupt(struct clock_even
 	struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);
 	ktime_t expires_next, now, entry_time, delta;
 	int retries = 0;
+	int raise;
 
 	BUG_ON(!cpu_base->hres_active);
 	cpu_base->nr_events++;
@@ -1465,7 +1465,7 @@ void hrtimer_interrupt(struct clock_even
 	 */
 	cpu_base->expires_next = KTIME_MAX;
 
-	__hrtimer_run_queues(cpu_base, now);
+	raise = __hrtimer_run_queues(cpu_base, now);
 
 	/* Reevaluate the clock bases for the next expiry */
 	expires_next = __hrtimer_get_next_event(cpu_base);
@@ -1476,6 +1476,8 @@ void hrtimer_interrupt(struct clock_even
 	cpu_base->expires_next = expires_next;
 	cpu_base->in_hrtirq = 0;
 	raw_spin_unlock(&cpu_base->lock);
+	if (raise)
+		raise_softirq_irqoff(HRTIMER_SOFTIRQ);
 
 	/* Reprogramming necessary ? */
 	if (!tick_program_event(expires_next, 0)) {
@@ -1552,6 +1554,7 @@ void hrtimer_run_queues(void)
 {
 	struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);
 	ktime_t now;
+	int raise;
 
 	if (__hrtimer_hres_active(cpu_base))
 		return;
@@ -1570,8 +1573,10 @@ void hrtimer_run_queues(void)
 
 	raw_spin_lock(&cpu_base->lock);
 	now = hrtimer_update_base(cpu_base);
-	__hrtimer_run_queues(cpu_base, now);
+	raise = __hrtimer_run_queues(cpu_base, now);
 	raw_spin_unlock(&cpu_base->lock);
+	if (raise)
+		raise_softirq_irqoff(HRTIMER_SOFTIRQ);
 }
 
 /*