linux-kernel - Re: [PATCH] cgroup: Add missing cpus_read_lock() to cgroup_attach_task

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Date:   Thu, 25 Aug 2022 07:44:36 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Imran Khan <imran.f.khan@...cle.com>,
        Xuewen Yan <xuewen.yan@...soc.com>,
        syzbot <syzbot+29d3a3b4d86c8136ad9e@...kaller.appspotmail.com>,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] cgroup: Add missing cpus_read_lock() to
 cgroup_attach_task_all()

On Thu, Aug 25, 2022 at 05:38:38PM +0900, Tetsuo Handa wrote:
> syzbot is hitting percpu_rwsem_assert_held(&cpu_hotplug_lock) warning at
> cpuset_attach() [1], for commit 4f7e7236435ca0ab ("cgroup: Fix
> threadgroup_rwsem <-> cpus_read_lock() deadlock") missed that
> cpuset_attach() is also called from cgroup_attach_task_all().
> Add cpus_read_lock() like what cgroup_procs_write_start() does.
> 
> Link: https://syzkaller.appspot.com/bug?extid=29d3a3b4d86c8136ad9e [1]
> Reported-by: syzbot <syzbot+29d3a3b4d86c8136ad9e@...kaller.appspotmail.com>
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Fixes: 4f7e7236435ca0ab ("cgroup: Fix threadgroup_rwsem <-> cpus_read_lock() deadlock")

Applied to cgroup/for-6.0-fixes and sent pull request.

> Waiting for test result from syzbot. Should we remove "static" from
> cgroup_attach_lock() and call from cgroup_attach_task_all() ?

Yeah, that probably is better. Can you spin up a follow up patch?

Thanks.

-- 
tejun