tick: Cleanup NOHZ per cpu data on cpu down

commit 4b0c0f294f60abcdd20994a8341a95c8ac5eeb96 upstream.

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: 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>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 793548cb5a9598a2ba82425a7ae916c486e516ef..e9a45f1a34f581d906ff462e5a9c3be54a2a0a7b 100644 (file)
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -833,7 +833,7 @@ 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