linux-kernel - Re: [PATCH v2 1/3] cgroup: Iterate tasks that did not finish do

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Message-ID: <20200212220306.GH80993@mtj.thefacebook.com>
Date:   Wed, 12 Feb 2020 17:03:06 -0500
From:   Tejun Heo <tj@...nel.org>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     cgroups@...r.kernel.org, alex.shi@...ux.alibaba.com, guro@...com,
        hannes@...xchg.org, kernel-team@...roid.com,
        linger.lee@...iatek.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, lizefan@...wei.com,
        matthias.bgg@...il.com, shuah@...nel.org, surenb@...gle.com,
        tomcherry@...gle.com
Subject: Re: [PATCH v2 1/3] cgroup: Iterate tasks that did not finish
 do_exit()

On Fri, Jan 24, 2020 at 12:40:15PM +0100, Michal Koutný wrote:
> PF_EXITING is set earlier than actual removal from css_set when a task
> is exitting. This can confuse cgroup.procs readers who see no PF_EXITING
> tasks, however, rmdir is checking against css_set membership so it can
> transitionally fail with EBUSY.
> 
> Fix this by listing tasks that weren't unlinked from css_set active
> lists.
> It may happen that other users of the task iterator (without
> CSS_TASK_ITER_PROCS) spot a PF_EXITING task before cgroup_exit(). This
> is equal to the state before commit c03cd7738a83 ("cgroup: Include dying
> leaders with live threads in PROCS iterations") but it may be reviewed
> later.
> 
> Reported-by: Suren Baghdasaryan <surenb@...gle.com>
> Fixes: c03cd7738a83 ("cgroup: Include dying leaders with live threads in PROCS iterations")
> Signed-off-by: Michal Koutný <mkoutny@...e.com>

Applied to cgroup/for-5.6-fixes.

Thanks.

-- 
tejun