linux-kernel - Re: [PATCH] cgroup: Remove duplicates in cgroup v1 tasks file

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Message-ID: <ZSQrJtNAw9K4nNiG@slm.duckdns.org>
Date:   Mon, 9 Oct 2023 06:32:38 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Firo Yang <firo.yang@...e.com>
Subject: Re: [PATCH] cgroup: Remove duplicates in cgroup v1 tasks file

On Mon, Oct 09, 2023 at 03:58:11PM +0200, Michal Koutný wrote:
> One PID may appear multiple times in a preloaded pidlist.
> (Possibly due to PID recycling but we have reports of the same
> task_struct appearing with different PIDs, thus possibly involving
> transfer of PID via de_thread().)
> 
> Because v1 seq_file iterator uses PIDs as position, it leads to
> a message:
> > seq_file: buggy .next function kernfs_seq_next did not update position index
> 
> Conservative and quick fix consists of removing duplicates from `tasks`
> file (as opposed to removing pidlists altogether). It doesn't affect
> correctness (it's sufficient to show a PID once), performance impact
> would be hidden by unconditional sorting of the pidlist already in place
> (asymptotically).
> 
> Link: https://lore.kernel.org/r/20230823174804.23632-1-mkoutny@suse.com/
> Suggested-by: Firo Yang <firo.yang@...e.com>
> Signed-off-by: Michal Koutný <mkoutny@...e.com>

Applied to cgroup/for-6.6-fixes.

Thanks.

-- 
tejun