From a51474db9378c81bf6a6f6a4399829ee32a53b68 Mon Sep 17 00:00:00 2001
From: kib <kib@FreeBSD.org>
Date: Wed, 29 Feb 2012 15:09:20 +0000
Subject: Always request exclusive lock for the lower vnode in nullfs_vget().
 The null_nodeget() requires exclusive lock on lowervp to be able to
 insmntque() new vnode.

Reported by:	rea
Tested by:	pho
MFC after:	1 week
---
 sys/fs/nullfs/null_vfsops.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/sys/fs/nullfs/null_vfsops.c b/sys/fs/nullfs/null_vfsops.c
index b422077..414d2e3 100644
--- a/sys/fs/nullfs/null_vfsops.c
+++ b/sys/fs/nullfs/null_vfsops.c
@@ -312,6 +312,12 @@ nullfs_vget(mp, ino, flags, vpp)
 	struct vnode **vpp;
 {
 	int error;
+
+	KASSERT((flags & LK_TYPE_MASK) != 0,
+	    ("nullfs_vget: no lock requested"));
+	flags &= ~LK_TYPE_MASK;
+	flags |= LK_EXCLUSIVE;
+
 	error = VFS_VGET(MOUNTTONULLMOUNT(mp)->nullm_vfs, ino, flags, vpp);
 	if (error)
 		return (error);
-- 
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