[PATCH] hrtimers: fix posix-timer requeue race

From: Steven Rostedtrostedt@goodmis.org <rostedt@goodmis.org>

CPU0 expires a posix-timer and runs the callback function.  The signal is
queued.

After releasing the posix-timer lock and before returning to hrtimer_run_queue
CPU0 gets interrupted.  CPU1 delivers the queued signal and rearms the timer.
CPU0 comes back to hrtimer_run_queue and sets the timer state to expired.

The next modification of the timer can result in an oops, because the state
information is wrong.

Keep track of state = RUNNING and check if the state has been in the return
path of hrtimer_run_queue.  In case the state has been changed, ignore a
restart request and do not touch the state variable.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 6 insertions, 0 deletions

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 089bfb1fa01a..c657f3d4924a 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -40,6 +40,7 @@ enum hrtimer_restart {
 enum hrtimer_state {
         HRTIMER_INACTIVE,       /* Timer is inactive */
         HRTIMER_EXPIRED,                /* Timer is expired */
+        HRTIMER_RUNNING,                /* Timer is running the callback function */
         HRTIMER_PENDING,                /* Timer is pending */
 };
 
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index f1c4155b49ac..f580dd9db286 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -550,6 +550,7 @@ static inline void run_hrtimer_queue(struct hrtimer_base *base)
                 fn = timer->function;
                 data = timer->data;
                 set_curr_timer(base, timer);
+                timer->state = HRTIMER_RUNNING;
                 __remove_hrtimer(timer, base);
                 spin_unlock_irq(&base->lock);
 
@@ -565,6 +566,10 @@ static inline void run_hrtimer_queue(struct hrtimer_base *base)
 
                 spin_lock_irq(&base->lock);
 
+                /* Another CPU has added back the timer */
+                if (timer->state != HRTIMER_RUNNING)
+                        continue;
+
                 if (restart == HRTIMER_RESTART)
                         enqueue_hrtimer(timer, base);
                 else