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: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index f992762d7f51c9e187160f8ee78543a5933cf679..25d34e1a791169bdfc24a0d7be8bb67ab670e8ea 100644 (file)
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -769,7 +769,7 @@ 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