linux-kernel - Re: cgroup_enable_task_cg_lists && PF_EXITING (Was: KCSAN: data-race in exit_signals / prepare

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Message-ID: <20191024175427.GC3622521@devbig004.ftw2.facebook.com>
Date:   Thu, 24 Oct 2019 10:54:27 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        akpm@...ux-foundation.org, arnd@...db.de, christian@...uner.io,
        deepa.kernel@...il.com, ebiederm@...ssion.com, elver@...gle.com,
        guro@...com, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: cgroup_enable_task_cg_lists && PF_EXITING (Was: KCSAN: data-race
 in exit_signals / prepare_signal)

Hello, Oleg.

On Mon, Oct 21, 2019 at 04:21:11PM +0200, Oleg Nesterov wrote:
> could you explain the usage of siglock/PF_EXITING in
> cgroup_enable_task_cg_lists() ?
> 
> PF_EXITING is protected by cgroup_threadgroup_rwsem, not by
> sighand->siglock.

Yeah, the optimization was added a really long time ago and I'm not
sure it was ever correct.  I'm removing it.  If this ever becomes a
problem (pretty unlikely), I think the right thing to do is adding a
boot param instead of trying to do this dynamically.

Thanks.

-- 
tejun