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

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Message-ID: <YovaKZV7IzQgCo9E@slm.duckdns.org>
Date:   Mon, 23 May 2022 09:02:01 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Tadeusz Struk <tadeusz.struk@...aro.org>
Cc:     Michal Koutný <mkoutny@...e.com>,
        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 Mon, May 23, 2022 at 12:00:06PM -0700, Tadeusz Struk wrote:
> 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.

Can you try holding an extra ref in the killed path?

Thanks.

-- 
tejun