linux-kernel - Re: [PATCH] Revert "exec: make de_thread() freezable (was: Re: Linux 4.20-rc4)

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Message-ID: <CAHk-=wgaEw566btStrWE+NOgPJLn1whS-Yw1-=K2Qr6MDvSZ+A@mail.gmail.com>
Date:   Tue, 4 Dec 2018 09:31:11 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     mhocko@...nel.org
Cc:     Ingo Molnar <mingo@...nel.org>, pavel@....cz,
        Oleg Nesterov <oleg@...hat.com>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        rafael.j.wysocki@...el.com, chanho.min@....com,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] Revert "exec: make de_thread() freezable (was: Re: Linux 4.20-rc4)

On Tue, Dec 4, 2018 at 1:58 AM Michal Hocko <mhocko@...nel.org> wrote:
>
> AFAIU both suspend and hibernation require the system to enter quiescent
> state with no task potentially interfering with suspended devices. And
> in this particular case those de-thread-ed threads will certainly not
> interfere so silencing the lockdep sounds like a reasonable workaround.

I still think it would be better to simply not freeze killed user processes.

We already  have things like

        if (test_tsk_thread_flag(p, TIF_MEMDIE))
                return false;

exactly because we do not want to freeze processes that are about to
die due to being killed. Very similar situation: we don't want to
freeze those processes, because doing so would halt them from freeing
the resources that may be needed for suspend or hibernate.

How about something like we set PF_NOFREEZE when we set PF_EXITING? At
that point we've pretty much turned into a kernel thread, no?

                Linus