From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Fri, 18 Aug 2017 10:09:09 +0200
Subject: kernel/hrtimer: migrate deferred timer on CPU down
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: b3c08bffdcdd23f1b3ca8d9c01e3b8a715e03d46
Patch-mainline: Queued in subsystem maintainer repository
References: SLE15 Realtime Extension

hrtimers, which were deferred to the softirq context, and expire between
softirq shutdown and hrtimer migration are dangling around. If the CPU
goes back up the list head will be initialized and this corrupts the
timer's list. It will remain unnoticed until a hrtimer_cancel().
This moves those timers so they will expire.

Cc: stable-rt@vger.kernel.org
Reported-by: Mike Galbraith <efault@gmx.de>
Tested-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 |    5 +++++
 1 file changed, 5 insertions(+)

--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1801,6 +1801,11 @@ static void migrate_hrtimer_list(struct
 		 */
 		enqueue_hrtimer(timer, new_base);
 	}
+#ifdef CONFIG_PREEMPT_RT_BASE
+	list_splice_tail(&old_base->expired, &new_base->expired);
+	if (!list_empty(&new_base->expired))
+		raise_softirq_irqoff(HRTIMER_SOFTIRQ);
+#endif
 }
 
 int hrtimers_dead_cpu(unsigned int scpu)