[PATCH] namei: revalidate negative dentry before return -ENOENT

["Yan, Zheng" <zyan@redhat.com>]

After commit 766c4cbf "namei: d_is_negative() should be checked
before ->d_seq validation", lookup_fast() can return -ENOENT without
revalidating the negative dentry. This breaks network filesystems
that allow creating/deleting files from multiple hosts.

Signed-off-by: Yan, Zheng <zyan@redhat.com>
---
 fs/namei.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 726d211..5ffbf53 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1558,8 +1558,6 @@ static int lookup_fast(struct nameidata *nd,
 		negative = d_is_negative(dentry);
 		if (read_seqcount_retry(&dentry->d_seq, seq))
 			return -ECHILD;
-		if (negative)
-			return -ENOENT;
 
 		/*
 		 * This sequence count validates that the parent had no
@@ -1580,6 +1578,10 @@ static int lookup_fast(struct nameidata *nd,
 				goto unlazy;
 			}
 		}
+
+		if (negative)
+			return -ENOENT;
+
 		path->mnt = mnt;
 		path->dentry = dentry;
 		if (likely(__follow_mount_rcu(nd, path, inode, seqp)))
-- 
1.9.3