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@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 7357842..13fdda1 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -857,6 +857,7 @@
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 @@
}
out:
mutex_unlock(&watchdog_proc_mutex);
+ put_online_cpus();
return err;
}
@@ -949,6 +951,7 @@
{
int err, old;
+ get_online_cpus();
mutex_lock(&watchdog_proc_mutex);
if (watchdog_suspended) {
@@ -974,6 +977,7 @@
}
out:
mutex_unlock(&watchdog_proc_mutex);
+ put_online_cpus();
return err;
}
@@ -988,6 +992,7 @@
{
int err;
+ get_online_cpus();
mutex_lock(&watchdog_proc_mutex);
if (watchdog_suspended) {
@@ -1015,6 +1020,7 @@
}
out:
mutex_unlock(&watchdog_proc_mutex);
+ put_online_cpus();
return err;
}