The patch titled
Subject: kernel/watchdog.c: avoid race between lockup detector suspend/resume and CPU hotplug
has been added to the -mm tree. Its filename is
watchdog-avoid-race-between-lockup-detector-suspend-resume-and-cpu-hotplug.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/watchdog-avoid-race-between-lockup-detector-suspend-resume-and-cpu-hotplug.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/watchdog-avoid-race-between-lockup-detector-suspend-resume-and-cpu-hotplug.patch
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------------------------------------------------------
From: Ulrich Obergfell <uobergfe@xxxxxxxxxx>
Subject: kernel/watchdog.c: avoid race between lockup detector suspend/resume and CPU hotplug
The lockup detector suspend/resume interface that was introduced by
8c073d27d7ad293bf ("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@xxxxxxxxxx>
Cc: Don Zickus <dzickus@xxxxxxxxxx>
Cc: Aaron Tomlin <atomlin@xxxxxxxxxx>
Cc: Ulrich Obergfell <uobergfe@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/watchdog.c | 2 ++
1 file changed, 2 insertions(+)
diff -puN kernel/watchdog.c~watchdog-avoid-race-between-lockup-detector-suspend-resume-and-cpu-hotplug kernel/watchdog.c
--- a/kernel/watchdog.c~watchdog-avoid-race-between-lockup-detector-suspend-resume-and-cpu-hotplug
+++ a/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)
_
Patches currently in -mm which might be from uobergfe@xxxxxxxxxx are
watchdog-fix-error-handling-in-proc_watchdog_thresh.patch
watchdog-move-watchdog_disable_all_cpus-outside-of-ifdef.patch
watchdog-implement-error-handling-in-update_watchdog_all_cpus-and-callers.patch
watchdog-implement-error-handling-in-lockup_detector_suspend.patch
watchdog-do-not-unpark-threads-in-watchdog_park_threads-on-error.patch
watchdog-avoid-race-between-lockup-detector-suspend-resume-and-cpu-hotplug.patch
watchdog-avoid-races-between-proc-handlers-and-cpu-hotplug.patch
watchdog-remove-getput_online_cpus-from-watchdog_parkunpark_threads.patch
watchdog-fix-race-between-proc_watchdog_thresh-and-watchdog_timer_fn.patch
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