linux-kernel - Re: [PATCH 2/3] cgroup: Iterate tasks that did not finish do

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Message-ID: <20200117172806.GK2677547@devbig004.ftw2.facebook.com>
Date:   Fri, 17 Jan 2020 09:28:06 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     cgroups@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
        Li Zefan <lizefan@...wei.com>, alex.shi@...ux.alibaba.com,
        guro@...com, 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, matthias.bgg@...il.com,
        shuah@...nel.org, tomcherry@...gle.com
Subject: Re: [PATCH 2/3] cgroup: Iterate tasks that did not finish do_exit()

On Fri, Jan 17, 2020 at 04:15:32PM +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.

Yeah, this looks fine to me.  Any chance you can order this before the
clean up so that we can mark it for -stable.

Thanks.

-- 
tejun