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authorUlrich Obergfell <uobergfe@redhat.com>2015-11-05 18:44:50 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2015-11-05 19:34:48 -0800
commit8614ddef82139d08234dbf681188f9bcddae9f03 (patch)
treedc10d978bad575ec2045f1605084485e95313806 /kernel/watchdog.c
parentee89e71eb091d3ef8ca2be8bd4ec77ccfa91334c (diff)
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>
Diffstat (limited to 'kernel/watchdog.c')
-rw-r--r--kernel/watchdog.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 7357842da933..13fdda1a4c91 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;
}