From ee89e71eb091d3ef8ca2be8bd4ec77ccfa91334c Mon Sep 17 00:00:00 2001
From: Ulrich Obergfell <uobergfe@redhat.com>
Date: Thu, 5 Nov 2015 18:44:47 -0800
Subject: [PATCH] kernel/watchdog.c: avoid race between lockup detector
suspend/resume and CPU hotplug
The lockup detector suspend/resume interface that was introduced by
commit 8c073d27d7ad ("watchdog: introduce watchdog_suspend() and
watchdog_resume()") does not protect itself against races with CPU
hotplug. Hence, theoretically it is possible that a new watchdog thread
is started on a hotplugged CPU while the lockup detector is suspended,
and the thread could thus interfere unexpectedly with the code that
requested to suspend the lockup detector.
Avoid the race by calling
get_online_cpus() in lockup_detector_suspend()
put_online_cpus() in lockup_detector_resume()
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>
---
kernel/watchdog.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 0a23125369f14d..7357842da933aa 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -719,6 +719,7 @@ int lockup_detector_suspend(void)
{
int ret = 0;
+ get_online_cpus();
mutex_lock(&watchdog_proc_mutex);
/*
* Multiple suspend requests can be active in parallel (counted by
@@ -759,6 +760,7 @@ void lockup_detector_resume(void)
watchdog_unpark_threads();
mutex_unlock(&watchdog_proc_mutex);
+ put_online_cpus();
}
static int update_watchdog_all_cpus(void)
--
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