From a2ff2643571ccddfcad6d00a633545607ce2b045 Mon Sep 17 00:00:00 2001
From: Mike Galbraith <efault@gmx.de>
Date: Sun, 3 Sep 2017 04:48:10 +0200
Subject: [PATCH 387/398] kernel/hrtimer/hotplug: don't wake ktimersoftd while
 holding the hrtimer base lock

kernel/hrtimer: don't wakeup a process while holding the hrtimer base lock
missed a path, namely hrtimers_dead_cpu() -> migrate_hrtimer_list().  Defer
raising softirq until after base lock has been released there as well.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/time/hrtimer.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 0bf61641cc6e..e0dcff3e78b7 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1865,7 +1865,7 @@ static void init_hrtimers_cpu(int cpu)
 
 #ifdef CONFIG_HOTPLUG_CPU
 
-static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
+static int migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
 				struct hrtimer_clock_base *new_base)
 {
 	struct hrtimer *timer;
@@ -1895,15 +1895,19 @@ static void migrate_hrtimer_list(struct hrtimer_clock_base *old_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);
+	/*
+	 * Tell the caller to raise HRTIMER_SOFTIRQ.  We can't safely
+	 * acquire ktimersoftd->pi_lock while the base lock is held.
+	 */
+	return !list_empty(&new_base->expired);
 #endif
+	return 0;
 }
 
 static void migrate_hrtimers(int scpu)
 {
 	struct hrtimer_cpu_base *old_base, *new_base;
-	int i;
+	int i, raise = 0;
 
 	BUG_ON(cpu_online(scpu));
 	tick_cancel_sched_timer(scpu);
@@ -1919,13 +1923,16 @@ static void migrate_hrtimers(int scpu)
 	raw_spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING);
 
 	for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
-		migrate_hrtimer_list(&old_base->clock_base[i],
-				     &new_base->clock_base[i]);
+		raise |= migrate_hrtimer_list(&old_base->clock_base[i],
+					      &new_base->clock_base[i]);
 	}
 
 	raw_spin_unlock(&old_base->lock);
 	raw_spin_unlock(&new_base->lock);
 
+	if (raise)
+		raise_softirq_irqoff(HRTIMER_SOFTIRQ);
+
 	/* Check, if we got expired work to do */
 	__hrtimer_peek_ahead_timers();
 	local_irq_enable();
-- 
2.14.4

