[tip:timers/urgent] tick: Cleanup NOHZ per cpu data on cpu down

[tip-bot for Thomas Gleixner <tipbot@zytor.com>]

Commit-ID:  ae7868e241c015aadc8632d9fe633a102a5918f6
Gitweb:     http://git.kernel.org/tip/ae7868e241c015aadc8632d9fe633a102a5918f6
Author:     Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Fri, 3 May 2013 15:02:50 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Sun, 5 May 2013 08:15:11 +0200

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
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1305031451561.2886@ionos
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/time/tick-common.c   | 1 +
 kernel/time/tick-internal.h | 6 ++++++
 kernel/time/tick-sched.c    | 7 +++++++
 3 files changed, 14 insertions(+)

diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 6176a3e..29b765d 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -387,6 +387,7 @@ static int tick_notify(struct notifier_block *nb, unsigned long reason,
 		tick_shutdown_broadcast_oneshot(dev);
 		tick_shutdown_broadcast(dev);
 		tick_shutdown(dev);
+		tick_shutdown_nohz(dev);
 		break;
 
 	case CLOCK_EVT_NOTIFY_SUSPEND:
diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h
index f0299ea..9644b29 100644
--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -144,3 +144,9 @@ static inline int tick_device_is_functional(struct clock_event_device *dev)
 #endif
 
 extern void do_timer(unsigned long ticks);
+
+#ifdef CONFIG_NO_HZ
+extern void tick_shutdown_nohz(unsigned int *cpup);
+#else
+static inline void tick_shutdown_nohz(unsigned int *cpup) { }
+#endif
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 225f8bf..e985ccd 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -797,6 +797,13 @@ static inline void tick_check_nohz(int cpu)
 	}
 }
 
+void tick_shutdown_nohz(unsigned int *cpup)
+{
+	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+
+	memset(ts, 0, sizeof(*ts));
+}
+
 #else
 
 static inline void tick_nohz_switch_to_nohz(void) { }