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Date: Tue, 3 Nov 2015 19:06:58 -0500
From: Tejun Heo <tj@kernel.org>
To: Jeff Layton <jlayton@poochiereds.net>
Cc: Chris Worley <chris.worley@primarydata.com>, linux-kernel@vger.kernel.org,
        bfields@fieldses.org,
        Michael Skralivetsky <michael.skralivetsky@primarydata.com>,
        Trond Myklebust <trond.myklebust@primarydata.com>,
        Shaohua Li <shli@fb.com>
Subject: Re: timer code oops when calling mod_delayed_work
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Hello, Jeff.

Can you please verify whether the following patch fixes the issue?

Thanks.

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 84190f0..566a282 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -970,12 +970,21 @@ EXPORT_SYMBOL(add_timer);
  */
 void add_timer_on(struct timer_list *timer, int cpu)
 {
-	struct tvec_base *base = per_cpu_ptr(&tvec_bases, cpu);
+	struct tvec_base *new_base = per_cpu_ptr(&tvec_bases, cpu);
+	struct tvec_base *base;
 	unsigned long flags;
 
 	timer_stats_timer_set_start_info(timer);
 	BUG_ON(timer_pending(timer) || !timer->function);
-	spin_lock_irqsave(&base->lock, flags);
+
+	base = lock_timer_base(timer, &flags);
+	if (base != new_base) {
+		timer->flags |= TIMER_MIGRATING;
+		spin_unlock(&base->lock);
+		base = new_base;
+		spin_lock(&base->lock);
+	}
+
 	timer->flags = (timer->flags & ~TIMER_BASEMASK) | cpu;
 	debug_activate(timer, timer->expires);
 	internal_add_timer(base, timer);