alarmtimer: Ensure RTC module is not unloaded

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-and-tested-by: Michal Simek <monstr@monstr.eu>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <john.stultz@linaro.org>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Link: http://lkml.kernel.org/r/20170820220146.30969-1-alexandre.belloni@free-electrons.com

diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index 73a2b47..ec09ce9 100644 (file)
--- 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"
 
@@ -103,6 +104,11 @@ 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);