linux-kernel - Re: [PATCH] cgroup: don't queue css_release

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Date:   Mon, 23 May 2022 12:00:06 -0700
From:   Tadeusz Struk <tadeusz.struk@...aro.org>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     Tejun Heo <tj@...nel.org>, Hillf Danton <hdanton@...a.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        syzbot+e42ae441c3b10acf9e9d@...kaller.appspotmail.com
Subject: Re: [PATCH] cgroup: don't queue css_release_work if one already
 pending

On 5/20/22 09:42, Michal Koutný wrote:
> On Fri, May 20, 2022 at 09:38:12AM -0700, Tadeusz Struk <tadeusz.struk@...aro.org> wrote:
>> as this is a result of enqueuing the same css->destroy_work onto the same WQ,
>> one on the rcu path and one on the css_release path.
>> I will prototype it today and test with syzbot.
> 
> In my understanding, you'd need two independent work_structs in a css,
> not two separate workqueues to put the single entry on.

Yes, separating the css_killed_ref and css_release paths with two separate work_structs
fixes the two syzbot list corruption issues [1]&[2].
I tested it on mainline v5.18.0 and v5.10.117
In case of [2] the mainline triggers an issue, but it is unrelated to list corruption.

[1] https://syzkaller.appspot.com/bug?id=e26e54d6eac9d9fb50b221ec3e4627b327465dbd
[2] https://syzkaller.appspot.com/bug?id=3c7ff113ccb695e839b859da3fc481c36eb1cfd5

I will send a patch soon.

-- 
Thanks,
Tadeusz