linux-kernel - [PATCH cgroup/for-4.7-fixes] cgroup: set css->id to -1 during init

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Message-ID: <20160526194213.GD23194@mtj.duckdns.org>
Date:	Thu, 26 May 2016 15:42:13 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Wenwei Tao <wwtao0320@....com>
Cc:	lizefan@...wei.com, hannes@...xchg.org, ww.tao0320@...il.com,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH cgroup/for-4.7-fixes] cgroup: set css->id to -1 during init

Hello,

A follow-up patch.  Will queue in cgroup/for-4.7-fixes.

Thanks.
------ 8< ------
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@...nel.org>
Cc: Wenwei Tao <ww.tao0320@...il.com>
Fixes: 01e586598b22 ("cgroup: release css->id after css_free")
Cc: stable@...r.kernel.org # v4.0+
---
 kernel/cgroup.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 789b84f..688eb0c 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++;