[PATCH] locking: Giving mutex warning more precisely in case of !lock->owner

[Chuansheng Liu <chuansheng.liu@intel.com>]

When enabling mutex debugging, in case the imbalanced mutex_unlock()
is called, we still get the warning like below:
[  364.208284] DEBUG_LOCKS_WARN_ON(lock->owner != current)

But in that case, it is due to imbalanced mutex_unlock calling, and
the lock->owner is NULL.

Here we can enhance the case to give the warning as below:
 DEBUG_LOCKS_WARN_ON(lock->owner == NULL)

Signed-off-by: Liu, Chuansheng <chuansheng.liu@intel.com>
---
 kernel/locking/mutex-debug.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c
index 7e3443f..b2a1b96 100644
--- a/kernel/locking/mutex-debug.c
+++ b/kernel/locking/mutex-debug.c
@@ -75,7 +75,12 @@ void debug_mutex_unlock(struct mutex *lock)
 		return;
 
 	DEBUG_LOCKS_WARN_ON(lock->magic != lock);
-	DEBUG_LOCKS_WARN_ON(lock->owner != current);
+
+	if (!lock->owner)
+		DEBUG_LOCKS_WARN_ON(lock->owner == NULL);
+	else
+		DEBUG_LOCKS_WARN_ON(lock->owner != current);
+
 	DEBUG_LOCKS_WARN_ON(!lock->wait_list.prev && !lock->wait_list.next);
 	mutex_clear_owner(lock);
 }
-- 
1.7.9.5