linux-kernel - [tip:timers/core] alarmtimer: Ensure RTC module is not unloaded

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Message-ID: <tip-51218298a25e6942957c5595f2abf130d47d5df9@git.kernel.org>
Date:   Thu, 31 Aug 2017 12:40:28 -0700
From:   tip-bot for Alexandre Belloni <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     monstr@...str.eu, hpa@...or.com,
        alexandre.belloni@...e-electrons.com, tglx@...utronix.de,
        sboyd@...eaurora.org, john.stultz@...aro.org, mingo@...nel.org,
        linux-kernel@...r.kernel.org
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@...e-electrons.com>
AuthorDate: Mon, 21 Aug 2017 00:01:46 +0200
Committer:  Thomas Gleixner <tglx@...utronix.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@...str.eu>
Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: John Stultz <john.stultz@...aro.org>
Cc: Stephen Boyd <sboyd@...eaurora.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);