From: Al Viro <viro@zeniv.linux.org.uk>
Date: Sun, 10 Nov 2019 11:53:27 -0500
Subject: cgroup: don't put ERR_PTR() into fc->root
Git-commit: 630faf81b3e61bcc90dc6d8b497800657d2752a5
Patch-mainline: 5.4-rc8
References: bnc#1151927 5.3.16

the caller of ->get_tree() expects NULL left there on error...

Reported-by: Thibaut Sautereau <thibaut@sautereau.fr>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 kernel/cgroup/cgroup.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2119,11 +2119,12 @@ int cgroup_do_get_tree(struct fs_context
 
 		nsdentry = kernfs_node_dentry(cgrp->kn, sb);
 		dput(fc->root);
-		fc->root = nsdentry;
 		if (IS_ERR(nsdentry)) {
-			ret = PTR_ERR(nsdentry);
 			deactivate_locked_super(sb);
+			ret = PTR_ERR(nsdentry);
+			nsdentry = NULL;
 		}
+		fc->root = nsdentry;
 	}
 
 	if (!ctx->kfc.new_sb_created)