[PATCH] fuse: fix occasional dentry leak when readdirplus is used

[Niels de Vos <ndevos@redhat.com>]

In case d_lookup() returns a dentry with d_inode == NULL, the dentry is
not returned with dput(). This results in triggering a BUG() in
shrink_dcache_for_umount_subtree():

  BUG: Dentry ...{i=0,n=...} still in use (1) [unmount of fuse fuse]

Reported-by: Justin Clift <jclift@redhat.com>
Signed-off-by: Niels de Vos <ndevos@redhat.com>

--
Reproducing the BUG() on kernels with fuse that support READDIRPLUS can
be done with the GlusterFS tests:
- http://www.gluster.org/community/documentation/index.php/Using_the_Gluster_Test_Framework

After some stressing of the VFS and fuse mountpoints, bug-860663.t will
hit the BUG(). It does not happen on running this test stand-alone.
---
 fs/fuse/dir.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 0eda527..da67a15 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1246,7 +1246,9 @@ static int fuse_direntplus_link(struct file *file,
 		if (err)
 			goto out;
 		dput(dentry);
-		dentry = NULL;
+	} else if (dentry) {
+		/* this dentry does not have a d_inode, just drop it */
+		dput(dentry);
 	}
 
 	dentry = d_alloc(parent, &name);
-- 
1.7.1