cgroup: set css->id to -1 during init

If percpu_ref initialization fails during css_create(), the free path
can end up trying to free css->id of zero.  As ID 0 is unused, it
doesn't cause a critical breakage but it does trigger a warning
message.  Fix it by setting css->id to -1 from init_and_link_css().

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Wenwei Tao <ww.tao0320@gmail.com>
Fixes: 01e586598b22 ("cgroup: release css->id after css_free")
Cc: stable@vger.kernel.org # v4.0+
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 789b84f973c9..688eb0cd1851 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -5063,6 +5063,7 @@ static void init_and_link_css(struct cgroup_subsys_state *css,
         memset(css, 0, sizeof(*css));
         css->cgroup = cgrp;
         css->ss = ss;
+        css->id = -1;
         INIT_LIST_HEAD(&css->sibling);
         INIT_LIST_HEAD(&css->children);
         css->serial_nr = css_serial_nr_next++;