linux-kernel - Re: [PATCH cgroup/for-4.10-fixes] cgroup/pids: remove spurious suspicious RCU usage warning

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Date:   Mon, 6 Mar 2017 15:12:00 -0500
From:   Tejun Heo <tj@...nel.org>
To:     cgroups@...r.kernel.org
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Mike Galbraith <efault@....de>, kernel-team@...com
Subject: Re: [PATCH cgroup/for-4.10-fixes] cgroup/pids: remove spurious
 suspicious RCU usage warning

On Wed, Mar 01, 2017 at 03:39:07PM -0500, Tejun Heo wrote:
> pids_can_fork() is special in that the css association is guaranteed
> to be stable throughout the function and thus doesn't need RCU
> protection around task_css access.  When determining the css to charge
> the pid, task_css_check() is used to override the RCU sanity check.
> 
> While adding a warning message on fork rejection from pids limit,
> 135b8b37bd91 ("cgroup: Add pids controller event when fork fails
> because of pid limit") incorrectly added a task_css access which is
> neither RCU protected or explicitly annotated.  This triggers the
> following suspicious RCU usage warning when RCU debugging is enabled.

Applied to cgroup/for-4.11-fixes.

-- 
tejun