Patchwork [3.5.y.z,extended,stable] Patch "hrtimer: Prevent hrtimer_enqueue_reprogram race" has been added to staging queue

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Submitter Luis Henriques
Date Feb. 26, 2013, 4:13 p.m.
Message ID <1361895197-27616-1-git-send-email-luis.henriques@canonical.com>
Download mbox | patch
Permalink /patch/223291/
State New
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Comments

Luis Henriques - Feb. 26, 2013, 4:13 p.m.
This is a note to let you know that I have just added a patch titled

    hrtimer: Prevent hrtimer_enqueue_reprogram race

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

From 233c19c09303a2284c03824b18b71b476154739d Mon Sep 17 00:00:00 2001
From: Leonid Shatz <leonid.shatz@ravellosystems.com>
Date: Mon, 4 Feb 2013 14:33:37 +0200
Subject: [PATCH] hrtimer: Prevent hrtimer_enqueue_reprogram race

commit b22affe0aef429d657bc6505aacb1c569340ddd2 upstream.

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>
Link: http://lkml.kernel.org/r/1359981217-389-1-git-send-email-izik.eidus@ravellosystems.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
 kernel/hrtimer.c | 36 ++++++++++++++++++------------------
 1 file changed, 18 insertions(+), 18 deletions(-)

--
1.8.1.2

Patch

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 @@  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);