[PATCH 3.13 065/163] alarmtimer: Lock k_itimer during timer callback

Kamal Mostafa kamal at canonical.com
Thu Oct 9 21:01:30 UTC 2014 -stable review patch.  If anyone has any objections, please let me know.


From: Richard Larocque <rlarocque at google.com>

commit 474e941bed9262f5fa2394f9a4a67e24499e5926 upstream.

Locks the k_itimer's it_lock member when handling the alarm timer's
expiry callback.

The regular posix timers defined in posix-timers.c have this lock held
during timout processing because their callbacks are routed through
posix_timer_fn().  The alarm timers follow a different path, so they
ought to grab the lock somewhere else.

Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Ingo Molnar <mingo at kernel.org>
Cc: Richard Cochran <richardcochran at gmail.com>
Cc: Prarit Bhargava <prarit at redhat.com>
Cc: Sharvil Nanavati <sharvil at google.com>
Signed-off-by: Richard Larocque <rlarocque at google.com>
Signed-off-by: John Stultz <john.stultz at linaro.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
 kernel/time/alarmtimer.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index f7bdb14..cd45a07 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -464,8 +464,12 @@ static enum alarmtimer_type clock2alarm(clockid_t clockid)
 static enum alarmtimer_restart alarm_handle_timer(struct alarm *alarm,
 							ktime_t now)
+	unsigned long flags;
 	struct k_itimer *ptr = container_of(alarm, struct k_itimer,
+	enum alarmtimer_restart result = ALARMTIMER_NORESTART;
+	spin_lock_irqsave(&ptr->it_lock, flags);
 	if ((ptr->it_sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE) {
 		if (posix_timer_event(ptr, 0) != 0)
@@ -475,9 +479,11 @@ static enum alarmtimer_restart alarm_handle_timer(struct alarm *alarm,
 	if (ptr->it.alarm.interval.tv64) {
 		ptr->it_overrun += alarm_forward(alarm, now,
+	spin_unlock_irqrestore(&ptr->it_lock, flags);
+	return result;

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