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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 4 Dec 2018 09:31:11 -0800
Message-ID: <CAHk-=wgaEw566btStrWE+NOgPJLn1whS-Yw1-=K2Qr6MDvSZ+A@mail.gmail.com>
Subject: Re: [PATCH] Revert "exec: make de_thread() freezable (was: Re: Linux 4.20-rc4)
To:     mhocko@kernel.org
Cc:     Ingo Molnar <mingo@kernel.org>, pavel@ucw.cz,
        Oleg Nesterov <oleg@redhat.com>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        rafael.j.wysocki@intel.com, chanho.min@lge.com,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>
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On Tue, Dec 4, 2018 at 1:58 AM Michal Hocko <mhocko@kernel.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