[PATCH] alarmtimer: ensure RTC module is not unloaded

[Alexandre Belloni <alexandre.belloni@free-electrons.com>]

When registering the rtc device to be used to handle alarm timers,
get_device is used to ensure the device doesn't go away but the module can
still be unloaded. Call try_module_get to ensure the rtc driver will not go
away.

Reported-by: Michal Simek <monstr@monstr.eu>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
---
 kernel/time/alarmtimer.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index 0b8ff7d257ea..1c682eef7e6b 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -28,6 +28,7 @@
 #include <linux/workqueue.h>
 #include <linux/freezer.h>
 #include <linux/compat.h>
+#include <linux/module.h>
 
 #include "posix-timers.h"
 
@@ -100,6 +101,11 @@ static int alarmtimer_rtc_add_device(struct device *dev,
 
 	spin_lock_irqsave(&rtcdev_lock, flags);
 	if (!rtcdev) {
+		if (!try_module_get(rtc->owner)) {
+			spin_unlock_irqrestore(&rtcdev_lock, flags);
+			return -1;
+		}
+
 		rtcdev = rtc;
 		/* hold a reference so it doesn't go away */
 		get_device(dev);
-- 
2.14.1