The patch titled
Subject: kernel/watchdog.c: avoid races between /proc handlers and CPU hotplug
has been added to the -mm tree. Its filename is
watchdog-avoid-races-between-proc-handlers-and-cpu-hotplug.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/watchdog-avoid-races-between-proc-handlers-and-cpu-hotplug.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/watchdog-avoid-races-between-proc-handlers-and-cpu-hotplug.patch
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------------------------------------------------------
From: Ulrich Obergfell <uobergfe@xxxxxxxxxx>
Subject: kernel/watchdog.c: avoid races between /proc handlers and CPU hotplug
The handler functions for watchdog parameters in /proc/sys/kernel do not
protect themselves against races with CPU hotplug. Hence, theoretically
it is possible that a new watchdog thread is started on a hotplugged CPU
while a parameter is being modified, and the thread could thus use a
parameter value that is 'in transition'.
For example, if 'watchdog_thresh' is being set to zero (note: this
disables the lockup detectors) the thread would erroneously use the value
zero as the sample period.
To avoid such races and to keep the /proc handler code consistent,
call
{get|put}_online_cpus() in proc_watchdog_common()
{get|put}_online_cpus() in proc_watchdog_thresh()
{get|put}_online_cpus() in proc_watchdog_cpumask()
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 | 6 ++++++
1 file changed, 6 insertions(+)
diff -puN kernel/watchdog.c~watchdog-avoid-races-between-proc-handlers-and-cpu-hotplug kernel/watchdog.c
--- a/kernel/watchdog.c~watchdog-avoid-races-between-proc-handlers-and-cpu-hotplug
+++ a/kernel/watchdog.c
@@ -857,6 +857,7 @@ static int proc_watchdog_common(int whic
int err, old, new;
int *watchdog_param = (int *)table->data;
+ get_online_cpus();
mutex_lock(&watchdog_proc_mutex);
if (watchdog_suspended) {
@@ -908,6 +909,7 @@ static int proc_watchdog_common(int whic
}
out:
mutex_unlock(&watchdog_proc_mutex);
+ put_online_cpus();
return err;
}
@@ -949,6 +951,7 @@ int proc_watchdog_thresh(struct ctl_tabl
{
int err, old;
+ get_online_cpus();
mutex_lock(&watchdog_proc_mutex);
if (watchdog_suspended) {
@@ -974,6 +977,7 @@ int proc_watchdog_thresh(struct ctl_tabl
}
out:
mutex_unlock(&watchdog_proc_mutex);
+ put_online_cpus();
return err;
}
@@ -988,6 +992,7 @@ int proc_watchdog_cpumask(struct ctl_tab
{
int err;
+ get_online_cpus();
mutex_lock(&watchdog_proc_mutex);
if (watchdog_suspended) {
@@ -1015,6 +1020,7 @@ int proc_watchdog_cpumask(struct ctl_tab
}
out:
mutex_unlock(&watchdog_proc_mutex);
+ put_online_cpus();
return err;
}
_
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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