linux-kernel - [patch-rt] hotplug, hrtimer: Migrate expired/deferred timers during cpu offline

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Date:   Fri, 11 Aug 2017 09:55:16 +0200
From:   Mike Galbraith <efault@....de>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: [patch-rt] hotplug, hrtimer: Migrate expired/deferred timers during
 cpu offline

The below fixes the list debug explosion up.

If we do not migrate expired/deferred timers during cpu offline, ->cb_entry
will be corrupted by online initialization of base->expired, leading to a
loud list debug complaint should someone call __remove_hrtimer() thereafter.

Signed-off-by: Mike Galvraith <efault@....de>
---
 kernel/time/hrtimer.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1802,6 +1802,19 @@ static void migrate_hrtimer_list(struct
 		 */
 		enqueue_hrtimer(timer, new_base);
 	}
+
+	/*
+	 * Finally, migrate any expired timers deferred by RT.
+	 */
+	while (!list_empty(&old_base->expired)) {
+		struct list_head *entry = old_base->expired.next;
+
+		timer = container_of(entry, struct hrtimer, cb_entry);
+		/* XXX: hm, perhaps defer again instead of enqueueing. */
+		__remove_hrtimer(timer, old_base, HRTIMER_STATE_ENQUEUED, 0);
+		timer->base = new_base;
+		enqueue_hrtimer(timer, new_base);
+	}
 }
 
 int hrtimers_dead_cpu(unsigned int scpu)