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 <[email protected]>
---
kernel/watchdog.c | 6 ++++++
1 file changed, 6 insertions(+)
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 @@ static int proc_watchdog_common(int which, struct ctl_table
*table, int write,
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 which, struct ctl_table
*table, int write,
}
out:
mutex_unlock(&watchdog_proc_mutex);
+ put_online_cpus();
return err;
}
@@ -949,6 +951,7 @@ int proc_watchdog_thresh(struct ctl_table *table, int write,
{
int err, old;
+ get_online_cpus();
mutex_lock(&watchdog_proc_mutex);
if (watchdog_suspended) {
@@ -974,6 +977,7 @@ int proc_watchdog_thresh(struct ctl_table *table, int write,
}
out:
mutex_unlock(&watchdog_proc_mutex);
+ put_online_cpus();
return err;
}
@@ -988,6 +992,7 @@ int proc_watchdog_cpumask(struct ctl_table *table, int
write,
{
int err;
+ get_online_cpus();
mutex_lock(&watchdog_proc_mutex);
if (watchdog_suspended) {
@@ -1015,6 +1020,7 @@ int proc_watchdog_cpumask(struct ctl_table *table, int
write,
}
out:
mutex_unlock(&watchdog_proc_mutex);
+ put_online_cpus();
return err;
}
--
1.7.11.7
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