linux-kernel - Re: [PATCH cgroup/for-5.5] cgroup: remove cgroup_enable_task_cg

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Message-ID: <20191025155224.GC6020@redhat.com>
Date:   Fri, 25 Oct 2019 17:52:25 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     Tejun Heo <tj@...nel.org>, dvyukov@...gle.com,
        Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        akpm@...ux-foundation.org, arnd@...db.de, deepa.kernel@...il.com,
        ebiederm@...ssion.com, elver@...gle.com, guro@...com,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        cgroups@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH cgroup/for-5.5] cgroup: remove
 cgroup_enable_task_cg_lists() optimization

On 10/25, Christian Brauner wrote:
>
> On Fri, Oct 25, 2019 at 04:13:25PM +0200, Oleg Nesterov wrote:
> > Almost every usage of task->flags (load or sore) can be reported as "data race".
> > 
> > Say, you do
> > 
> > 	if (task->flags & PF_KTHREAD)
> > 
> > while this task does
> > 
> > 	current->flags |= PF_FREEZER_SKIP;
> > 	schedule().
> > 
> > this is data race.
> 
> Right, but I thought we agreed on WONTFIX in those scenarios?
> The alternative is to READ_ONCE()/WRITE_ONCE() all of these.

Well, in my opinion this is WONTFIX, but I won't argue if someone
adds _ONCE to all of these. Same for task->state, exit_state, and
more.

Oleg.