kill-the-bkl/reiserfs: panic in case of lock imbalance

Until now, trying to unlock the reiserfs write lock whereas the current
task doesn't hold it lead to a simple warning.
We should actually warn and panic in this case to avoid the user datas
to reach an unstable state.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jeff Mahoney <jeffm@suse.com>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Alexander Beregalov <a.beregalov@gmail.com>
Cc: Laurent Riffard <laurent.riffard@free.fr>

fs/reiserfs/lock.c

@@ -37,11 +37,10 @@ void reiserfs_write_unlock(struct super_block *s)
 
 	/*
 	 * Are we unlocking without even holding the lock?
-	 * Such a situation could even raise a BUG() if we don't
-	 * want the data become corrupted
+	 * Such a situation must raise a BUG() if we don't want
+	 * to corrupt the data.
 	 */
-	WARN_ONCE(sb_i->lock_owner != current,
-		  "Superblock write lock imbalance");
+	BUG_ON(sb_i->lock_owner != current);
 
 	if (--sb_i->lock_depth == -1) {
 		sb_i->lock_owner = NULL;