[PATCH vfs/for-next v2] cgroup: fix top cgroup refcnt leak

[Andrei Vagin <avagin@gmail.com>]

It looks like the c6b3d5bcd67c ("cgroup: fix top cgroup refcnt leak")
commit was reverted by mistake.

$ mkdir /tmp/cgroup
$ mkdir /tmp/cgroup2
$ mount -t cgroup -o none,name=test test /tmp/cgroup
$ mount -t cgroup -o none,name=test test /tmp/cgroup2
$ umount /tmp/cgroup
$ umount /tmp/cgroup2
$ cat /proc/self/cgroup | grep test
12:name=test:/

You can see the test cgroup was not freed.

Cc: Li Zefan <lizefan@huawei.com>
Fixes: aea3f2676c83 ("kernfs, sysfs, cgroup, intel_rdt: Support fs_context")
Signed-off-by: Andrei Vagin <avagin@gmail.com>
---

v2: clean up code and add the vfs/for-next tag

 kernel/cgroup/cgroup.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index fb0717696895..f63974a3725f 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2047,6 +2047,9 @@ int cgroup_do_get_tree(struct fs_context *fc)
 	ret = 0;
 	if (ctx->kfc.new_sb_created)
 		goto out_cgrp;
+	else
+		cgroup_put(&ctx->root->cgrp);
+
 	apply_cgroup_root_flags(ctx->flags);
 	return 0;
 
-- 
2.17.2