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Subject[tip:timers/core] alarmtimer: Ensure RTC module is not unloaded
Commit-ID:  51218298a25e6942957c5595f2abf130d47d5df9
Gitweb: http://git.kernel.org/tip/51218298a25e6942957c5595f2abf130d47d5df9
Author: Alexandre Belloni <alexandre.belloni@free-electrons.com>
AuthorDate: Mon, 21 Aug 2017 00:01:46 +0200
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 31 Aug 2017 21:36:45 +0200

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

---
kernel/time/alarmtimer.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index 73a2b47..ec09ce9 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"

@@ -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);
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