From 9ce7379778e7db8354fc0eba26bebf8ba4341e93 Mon Sep 17 00:00:00 2001
From: Peter Holm <pho@FreeBSD.org>
Date: Mon, 24 Oct 2011 10:35:37 +0000
Subject: [PATCH] Only unlock if the lock is exclusive.

Reported by:	Subbsd <subbsd gmail com>
Discussed with:	kib
---
 sys/fs/nullfs/null_vfsops.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/sys/fs/nullfs/null_vfsops.c b/sys/fs/nullfs/null_vfsops.c
index e39dd8f892c..97f8f133b05 100644
--- a/sys/fs/nullfs/null_vfsops.c
+++ b/sys/fs/nullfs/null_vfsops.c
@@ -104,11 +104,10 @@ nullfs_mount(struct mount *mp)
 		return (EINVAL);
 
 	/*
-	 * Unlock lower node to avoid deadlock.
-	 * (XXX) VOP_ISLOCKED is needed?
+	 * Unlock lower node to avoid possible deadlock.
 	 */
 	if ((mp->mnt_vnodecovered->v_op == &null_vnodeops) &&
-		VOP_ISLOCKED(mp->mnt_vnodecovered)) {
+	    VOP_ISLOCKED(mp->mnt_vnodecovered) == LK_EXCLUSIVE) {
 		VOP_UNLOCK(mp->mnt_vnodecovered, 0);
 		isvnunlocked = 1;
 	}