[3.13.y.z extended stable] Patch "alarmtimer: Lock k_itimer during timer callback" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    alarmtimer: Lock k_itimer during timer callback

to the linux-3.13.y-queue branch of the 3.13.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-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.9.

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

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From addc3fff5e4f41b60fda594db87e3264033ee7e4 Mon Sep 17 00:00:00 2001
From: Richard Larocque <rlarocque at google.com>
Date: Tue, 9 Sep 2014 18:31:05 -0700
Subject: alarmtimer: Lock k_itimer during timer callback

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,
 						it.alarm.alarmtimer);
+	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)
 			ptr->it_overrun++;
@@ -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,
 						ptr->it.alarm.interval);
-		return ALARMTIMER_RESTART;
+		result = ALARMTIMER_RESTART;
 	}
-	return ALARMTIMER_NORESTART;
+	spin_unlock_irqrestore(&ptr->it_lock, flags);
+
+	return result;
 }

 /**
--
1.9.1