Commit b22affe0 authored by Leonid Shatz's avatar Leonid Shatz Committed by Thomas Gleixner
Browse files

hrtimer: Prevent hrtimer_enqueue_reprogram race 



hrtimer_enqueue_reprogram contains a race which could result in
timer.base switch during unlock/lock sequence.

hrtimer_enqueue_reprogram is releasing the lock protecting the timer
base for calling raise_softirq_irqsoff() due to a lock ordering issue
versus rq->lock.

If during that time another CPU calls __hrtimer_start_range_ns() on
the same hrtimer, the timer base might switch, before the current CPU
can lock base->lock again and therefor the unlock_timer_base() call
will unlock the wrong lock.

[ tglx: Added comment and massaged changelog ]

Signed-off-by: default avatarLeonid Shatz <leonid.shatz@ravellosystems.com>
Signed-off-by: default avatarIzik Eidus <izik.eidus@ravellosystems.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/1359981217-389-1-git-send-email-izik.eidus@ravellosystems.com


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 90889a63

kernel/hrtimer.c

+18 −18
Original line number Diff line number Diff line
@@ -640,21 +640,9 @@ static inline void hrtimer_init_hres(struct hrtimer_cpu_base *base) 
 * and expiry check is done in the hrtimer_interrupt or in the softirq.

 */

static inline int hrtimer_enqueue_reprogram(struct hrtimer *timer,

					    struct hrtimer_clock_base *base,

					    int wakeup)

					    struct hrtimer_clock_base *base)

{

	if (base->cpu_base->hres_active && hrtimer_reprogram(timer, base)) {

		if (wakeup) {

			raw_spin_unlock(&base->cpu_base->lock);

			raise_softirq_irqoff(HRTIMER_SOFTIRQ);

			raw_spin_lock(&base->cpu_base->lock);

		} else

			__raise_softirq_irqoff(HRTIMER_SOFTIRQ);



		return 1;

	}



	return 0;

	return base->cpu_base->hres_active && hrtimer_reprogram(timer, base);

}



static inline ktime_t hrtimer_update_base(struct hrtimer_cpu_base *base)
@@ -735,8 +723,7 @@ static inline int hrtimer_switch_to_hres(void) { return 0; } 
static inline void

hrtimer_force_reprogram(struct hrtimer_cpu_base *base, int skip_equal) { }

static inline int hrtimer_enqueue_reprogram(struct hrtimer *timer,

					    struct hrtimer_clock_base *base,

					    int wakeup)

					    struct hrtimer_clock_base *base)

{

	return 0;

}
@@ -995,8 +982,21 @@ int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim, 
	 *

	 * XXX send_remote_softirq() ?

	 */

	if (leftmost && new_base->cpu_base == &__get_cpu_var(hrtimer_bases))

		hrtimer_enqueue_reprogram(timer, new_base, wakeup);

	if (leftmost && new_base->cpu_base == &__get_cpu_var(hrtimer_bases)

		&& hrtimer_enqueue_reprogram(timer, new_base)) {

		if (wakeup) {

			/*

			 * We need to drop cpu_base->lock to avoid a

			 * lock ordering issue vs. rq->lock.

			 */

			raw_spin_unlock(&new_base->cpu_base->lock);

			raise_softirq_irqoff(HRTIMER_SOFTIRQ);

			local_irq_restore(flags);

			return ret;

		} else {

			__raise_softirq_irqoff(HRTIMER_SOFTIRQ);

		}

	}



	unlock_hrtimer_base(timer, &flags);

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