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

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Message-ID: <20191025125606.GI3622521@devbig004.ftw2.facebook.com>
Date:   Fri, 25 Oct 2019 05:56:06 -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, cgroups@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH cgroup/for-5.5] cgroup: remove
 cgroup_enable_task_cg_lists() optimization

On Thu, Oct 24, 2019 at 12:03:51PM -0700, Tejun Heo wrote:
> cgroup_enable_task_cg_lists() is used to lazyily initialize task
> cgroup associations on the first use to reduce fork / exit overheads
> on systems which don't use cgroup.  Unfortunately, locking around it
> has never been actually correct and its value is dubious given how the
> vast majority of systems use cgroup right away from boot.
> 
> This patch removes the optimization.  For now, replace the cg_list
> based branches with WARN_ON_ONCE()'s to be on the safe side.  We can
> simplify the logic further in the future.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Reported-by: Oleg Nesterov <oleg@...hat.com>

Applying to cgroup/for-5.5.

Thanks.

-- 
tejun