linux-kernel - Re: [PATCH 0/2] Don't show PF_IO

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Date:   Fri, 26 Mar 2021 12:59:17 +0100
From:   Stefan Metzmacher <metze@...ba.org>
To:     Jens Axboe <axboe@...nel.dk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     io-uring <io-uring@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH 0/2] Don't show PF_IO_WORKER in /proc/<pid>/task/

Hi Jens,

>> And /proc/$iothread/ should be read only and owned by root with
>> "cmdline" and "exe" being empty.
> 
> I know you brought this one up as part of your series, not sure I get
> why you want it owned by root and read-only? cmdline and exe, yeah those
> could be hidden, but is there really any point?
> 
> Maybe I'm missing something here, if so, do clue me in!

I looked through /proc and I think it's mostly similar to
the unshare() case, if userspace wants to do stupid things
like changing "comm" of iothreads, it gets what was asked for.

But the "cmdline" hiding would be very useful.

While most tools use "comm", by default.

ps -eLf or 'iotop' use "cmdline".

Some processes use setproctitle to change "cmdline" in order
to identify the process better, without the 15 chars comm restriction,
that's why I very often press 'c' in 'top' to see the cmdline,
in that case it would be very helpful to see '[iou-wrk-1234]'
instead of the seeing the cmdline.

So I'd very much prefer if this could be applied:
https://lore.kernel.org/io-uring/d4487f959c778d0b1d4c5738b75bcff17d21df5b.1616197787.git.metze@samba.org/T/#u

If you want I can add a comment and a more verbose commit message...

metze