linux-kernel - [PATCH 4/4] watchdog: fix race between proc_watchdog_thresh() and watchdog_timer

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Message-Id: <1446564061-3379-5-git-send-email-uobergfe@redhat.com>
Date:	Tue,  3 Nov 2015 16:21:01 +0100
From:	Ulrich Obergfell <uobergfe@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	akpm@...ux-foundation.org, dzickus@...hat.com, atomlin@...hat.com,
	uobergfe@...hat.com
Subject: [PATCH 4/4] watchdog: fix race between proc_watchdog_thresh() and watchdog_timer_fn()

Theoretically it is possible that the watchdog timer expires
right at the time when a user sets 'watchdog_thresh' to zero
(note: this disables the lockup detectors). In this scenario,
the is_softlockup() function - which is called by the timer -
could produce a false positive.

Fix this by checking the current value of 'watchdog_thresh'.

Signed-off-by: Ulrich Obergfell <uobergfe@...hat.com>
---
 kernel/watchdog.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 84c4744..18f34cf 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -289,7 +289,7 @@ static int is_softlockup(unsigned long touch_ts)
 {
 	unsigned long now = get_timestamp();
 
-	if (watchdog_enabled & SOFT_WATCHDOG_ENABLED) {
+	if ((watchdog_enabled & SOFT_WATCHDOG_ENABLED) && watchdog_thresh){
 		/* Warn about unreasonable delays. */
 		if (time_after(now, touch_ts + get_softlockup_thresh()))
 			return now - touch_ts;
-- 
1.7.11.7

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