fuse: nlookup missing decrement in fuse_direntplus_link

commit b8bd342 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
gluster/glusterfs#4081

Signed-off-by: ruanmeisi <[email protected]>
Fixes: 0b05b18 ("fuse: implement NFS-like readdirplus support")
Cc: <[email protected]> # v3.9
Signed-off-by: Miklos Szeredi <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: ruanmeisi

fs/fuse/dir.c

@@ -1314,8 +1314,16 @@ static int fuse_direntplus_link(struct file *file,
 			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);