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

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Date:   Thu, 21 Apr 2022 14:00:56 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     Tadeusz Struk <tadeusz.struk@...aro.org>, cgroups@...r.kernel.org,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Christian Brauner <brauner@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        syzbot+e42ae441c3b10acf9e9d@...kaller.appspotmail.com
Subject: Re: [PATCH] cgroup: don't queue css_release_work if one already
 pending

On Thu, Apr 14, 2022 at 06:44:09PM +0200, Michal Koutný wrote:
> I suspect the double-queuing is a result of the fact that there exists
> only the single reference to the css->refcnt. I.e. it's
> percpu_ref_kill_and_confirm()'d and released both at the same time.
> 
> (Normally (when not killing the last reference), css->destroy_work reuse
> is not a problem because of the sequenced chain
> css_killed_work_fn()->css_put()->css_release().)

If this is the case, we need to hold an extra reference to be put by the
css_killed_work_fn(), right?

Thanks.

-- 
tejun