From: Ulrich Obergfell <uobergfe@redhat.com>
Date: Fri, 6 Nov 2015 02:44:56 +0000 (-0800)
Subject: kernel/watchdog.c: fix race between proc_watchdog_thresh() and watchdog_timer_fn()
X-Git-Tag: v4.4-rc1~99^2~136
X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=39d2da2161d35de301ec5397ce9103c68b883054;p=linux-2.6-block.git

kernel/watchdog.c: 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@redhat.com>
Acked-by: Don Zickus <dzickus@redhat.com>
Reviewed-by: Aaron Tomlin <atomlin@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 84c4744d1977..18f34cf75f74 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;