Fix unbalanced helper_lock in kernel/kmod.c

call_usermodehelper_exec() has an exit path that can leave the
helper_lock() call at the top of the routine unbalanced.  The attached
patch fixes this issue.

Signed-off-by: Nigel Cunningham <nigel@tuxonice.net>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/kmod.c

@@ -451,13 +451,11 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info,
 			     enum umh_wait wait)
 {
 	DECLARE_COMPLETION_ONSTACK(done);
-	int retval;
+	int retval = 0;
 
 	helper_lock();
-	if (sub_info->path[0] == '\0') {
-		retval = 0;
+	if (sub_info->path[0] == '\0')
 		goto out;
-	}
 
 	if (!khelper_wq || usermodehelper_disabled) {
 		retval = -EBUSY;
@@ -469,12 +467,13 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info,
 
 	queue_work(khelper_wq, &sub_info->work);
 	if (wait == UMH_NO_WAIT)	/* task has freed sub_info */
-		return 0;
+		goto unlock;
 	wait_for_completion(&done);
 	retval = sub_info->retval;
 
 out:
 	call_usermodehelper_freeinfo(sub_info);
+unlock:
 	helper_unlock();
 	return retval;
 }