linux-kernel - Re: [PATCH 2/2] cgroup: Use separate work structs on css release path

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Message-ID: <Ypf5jpI7dSmpi4W0@slm.duckdns.org>
Date:   Wed, 1 Jun 2022 13:43:10 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Tadeusz Struk <tadeusz.struk@...aro.org>
Cc:     Michal Koutný <mkoutny@...e.com>,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Bui Quang Minh <minhquangbui99@...il.com>
Subject: Re: [PATCH 2/2] cgroup: Use separate work structs on css release path

On Wed, Jun 01, 2022 at 04:37:17PM -0700, Tadeusz Struk wrote:
> Yes, but as far as I can see the percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn)
> doesn't change the value of the refcnt, it just causes the css_killed_ref_fn() to be called

Yeah, the base ref is special for percpu_ref.

> on it. Only css_get() & css_put() modify the refcnt value.
> And for the "free the thing" the css_killed_work_fn() does that.
> It calls offline_css(css) and css_put(css) for the whole css hierarchy.

Yeah, the freeing path depends on the css_put(css) invoking css_release()
which schedules the work item which actually frees. Am I misunderstanding
something here?

Thanks.

-- 
tejun