linux-kernel - Re: [PATCH?] race between cgroup_subsys->fork() and cgroup

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Message-ID: <20151126153609.GA23581@redhat.com>
Date:	Thu, 26 Nov 2015 16:36:09 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Aleksa Sarai <cyphar@...har.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Li Zefan <lizefan@...wei.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH?] race between cgroup_subsys->fork() and
	cgroup_migrate()

On 11/25, Tejun Heo wrote:
>
> On Wed, Nov 25, 2015 at 02:51:38PM -0500, Tejun Heo wrote:
> > Sounds perfect.  As this needs to go through -stable, can you please
> > resend the patch with proper description and SOB?  Please also update
> > the now incorrect comment in can_attach.

OK, will do tomorrow (sorry, can't do today).

> Ooh, the patch triggers RCU warning from task_css().  It's spurious
> and I think the right thing to do at least for now is using
> task_css_check() and explain what's going on.

WARN_ON() in pids_fork() I guess. Thanks. I didn't expect you will actually
apply this patch, I didn't even try to compile it ;)

Plus this patch forgets to unconditionalize another threadgroup_change_end()
in the error path of copy_process().

Again, if we do this, we can make other cleanups/simplifications. For example,
we can kill cgrp_ss_priv[CGROUP_CANFORK_COUNT] in copy_process().

But I see another email from you, will reply in a minute.

Oleg.

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