[PATCH] hrtimers: fix reprogramming SMP race

hrtimer_start() incorrectly set the 'reprogram' flag to enqueue_hrtimer(),
which should only be 1 if the hrtimer is queued to the current CPU.

Doing otherwise could result in a reprogramming of the current CPU's
clockevents device, with a timer that is not queued to it - resulting in a
bogus next expiry value.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Michal Piotrowski <michal.k.k.piotrowski@gmail.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/hrtimer.c

@@ -814,7 +814,12 @@ hrtimer_start(struct hrtimer *timer, ktime_t tim, const enum hrtimer_mode mode)
 
 	timer_stats_hrtimer_set_start_info(timer);
 
-	enqueue_hrtimer(timer, new_base, base == new_base);
+	/*
+	 * Only allow reprogramming if the new base is on this CPU.
+	 * (it might still be on another CPU if the timer was pending)
+	 */
+	enqueue_hrtimer(timer, new_base,
+			new_base->cpu_base == &__get_cpu_var(hrtimer_bases));
 
 	unlock_hrtimer_base(timer, &flags);