watchdog: update watchdog attributes atomically

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>

1 files changed, 5 insertions, 2 deletions

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 51c4f34d258e..ced7d0609931 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -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 */