linux-kernel - Re: cgroup: WARNING in cgroup_kill

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Message-ID: <20170306215515.GH26127@htj.duckdns.org>
Date:   Mon, 6 Mar 2017 16:55:15 -0500
From:   Tejun Heo <tj@...nel.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Zefan Li <lizefan@...wei.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>, jweiner@...com,
        LKML <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: cgroup: WARNING in cgroup_kill_sb

Hello, Dmitry.

Can you please see whether the following patch resolves the issue?
I'm a bit nervous about it ending up in circular dependency, but I
*think* it should be okay.

Thanks.

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 0125589..9c40421 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1820,6 +1820,8 @@ static void cgroup_kill_sb(struct super_block *sb)
 	struct kernfs_root *kf_root = kernfs_root_from_sb(sb);
 	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
 
+	mutex_lock(&cgroup_mutex);
+
 	/*
 	 * If @root doesn't have any mounts or children, start killing it.
 	 * This prevents new mounts by disabling percpu_ref_tryget_live().
@@ -1834,6 +1836,8 @@ static void cgroup_kill_sb(struct super_block *sb)
 		percpu_ref_kill(&root->cgrp.self.refcnt);
 
 	kernfs_kill_sb(sb);
+
+	mutex_unlock(&cgroup_mutex);
 }
 
 struct file_system_type cgroup_fs_type = {