watchdog: update watchdog attributes atomically
authorMichal Hocko <mhocko@suse.cz>
Tue, 24 Sep 2013 22:27:29 +0000 (15:27 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Wed, 25 Sep 2013 00:00:25 +0000 (17:00 -0700)
proc_dowatchdog doesn't synchronize multiple callers which might lead to
confusion when two parallel callers might confuse watchdog_enable_all_cpus
resp watchdog_disable_all_cpus (eg watchdog gets enabled even if
watchdog_thresh was set to 0 already).

This patch adds a local mutex which synchronizes callers to the sysctl
handler.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Don Zickus <dzickus@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kernel/watchdog.c

index 51c4f34d258ea397266e0dd1a96a16436415a38f..ced7d06099313c4a451be4718633dfd39876f6eb 100644 (file)
@@ -520,13 +520,15 @@ int proc_dowatchdog(struct ctl_table *table, int write,
                    void __user *buffer, size_t *lenp, loff_t *ppos)
 {
        int err, old_thresh, old_enabled;
+       static DEFINE_MUTEX(watchdog_proc_mutex);
 
+       mutex_lock(&watchdog_proc_mutex);
        old_thresh = ACCESS_ONCE(watchdog_thresh);
        old_enabled = ACCESS_ONCE(watchdog_user_enabled);
 
        err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
        if (err || !write)
-               return err;
+               goto out;
 
        set_sample_period();
        /*
@@ -544,7 +546,8 @@ int proc_dowatchdog(struct ctl_table *table, int write,
                watchdog_thresh = old_thresh;
                watchdog_user_enabled = old_enabled;
        }
-
+out:
+       mutex_unlock(&watchdog_proc_mutex);
        return err;
 }
 #endif /* CONFIG_SYSCTL */