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: Leonid Shatz <leonid.shatz@ravellosystems.com>
Signed-off-by: Izik 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: Thomas Gleixner <tglx@linutronix.de>
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 6db7a5e..cdd5607 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -640,21 +640,9 @@
* 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 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 @@
*
* 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);