From 4b0c0f294f60abcdd20994a8341a95c8ac5eeb96 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Fri, 3 May 2013 15:02:50 +0200
Subject: tick: Cleanup NOHZ per cpu data on cpu down

Prarit reported a crash on CPU offline/online. The reason is that on
CPU down the NOHZ related per cpu data of the dead cpu is not cleaned
up. If at cpu online an interrupt happens before the per cpu tick
device is registered the irq_enter() check potentially sees stale data
and dereferences a NULL pointer.

Cleanup the data after the cpu is dead.

Reported-by: Prarit Bhargava <prarit@redhat.com>
Cc: stable@vger.kernel.org
Cc: Mike Galbraith <bitbucket@online.de>
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1305031451561.2886@ionos
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 225f8bf..0eed1db 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -904,7 +904,7 @@ void tick_cancel_sched_timer(int cpu)
 		hrtimer_cancel(&ts->sched_timer);
 # endif
 
-	ts->nohz_mode = NOHZ_MODE_INACTIVE;
+	memset(ts, 0, sizeof(*ts));
 }
 #endif
 
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