[PATCH 4.19 18/25] fuse: nlookup missing decrement in fuse_direntplus_link

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: ruanmeisi <ruan.meisi@zte.com.cn>

commit b8bd342d50cbf606666488488f9fea374aceb2d5 upstream.

During our debugging of glusterfs, we found an Assertion failed error:
inode_lookup >= nlookup, which was caused by the nlookup value in the
kernel being greater than that in the FUSE file system.

The issue was introduced by fuse_direntplus_link, where in the function,
fuse_iget increments nlookup, and if d_splice_alias returns failure,
fuse_direntplus_link returns failure without decrementing nlookup
https://github.com/gluster/glusterfs/pull/4081

Signed-off-by: ruanmeisi <ruan.meisi@zte.com.cn>
Fixes: 0b05b18381ee ("fuse: implement NFS-like readdirplus support")
Cc: <stable@vger.kernel.org> # v3.9
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/fuse/dir.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1314,8 +1314,16 @@ retry:
 			dput(dentry);
 			dentry = alias;
 		}
-		if (IS_ERR(dentry))
+		if (IS_ERR(dentry)) {
+			if (!IS_ERR(inode)) {
+				struct fuse_inode *fi = get_fuse_inode(inode);
+
+				spin_lock(&fc->lock);
+				fi->nlookup--;
+				spin_unlock(&fc->lock);
+			}
 			return PTR_ERR(dentry);
+		}
 	}
 	if (fc->readdirplus_auto)
 		set_bit(FUSE_I_INIT_RDPLUS, &get_fuse_inode(inode)->state);