cifs: release cached dentries only if mount is complete

During cifs_kill_sb, we first dput all the dentries that we have cached.
However this function can also get called for mount failures.
So dput the cached dentries only if the filesystem mount is complete.
i.e. cifs_sb->root is populated.

Fixes: 5e9c89d4 ("cifs: Grab a reference for the dentry of the cached directory during the lifetime of the cache")
Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/cifsfs.c

@@ -266,22 +266,24 @@ static void cifs_kill_sb(struct super_block *sb)
 	 * before we kill the sb.
 	 */
 	if (cifs_sb->root) {
+		node = rb_first(root);
+		while (node != NULL) {
+			tlink = rb_entry(node, struct tcon_link, tl_rbnode);
+			tcon = tlink_tcon(tlink);
+			cfid = &tcon->crfid;
+			mutex_lock(&cfid->fid_mutex);
+			if (cfid->dentry) {
+				dput(cfid->dentry);
+				cfid->dentry = NULL;
+			}
+			mutex_unlock(&cfid->fid_mutex);
+			node = rb_next(node);
+		}
+
+		/* finally release root dentry */
 		dput(cifs_sb->root);
 		cifs_sb->root = NULL;
 	}
-	node = rb_first(root);
-	while (node != NULL) {
-		tlink = rb_entry(node, struct tcon_link, tl_rbnode);
-		tcon = tlink_tcon(tlink);
-		cfid = &tcon->crfid;
-		mutex_lock(&cfid->fid_mutex);
-		if (cfid->dentry) {
-			dput(cfid->dentry);
-			cfid->dentry = NULL;
-		}
-		mutex_unlock(&cfid->fid_mutex);
-		node = rb_next(node);
-	}
 
 	kill_anon_super(sb);
 	cifs_umount(cifs_sb);