linux-kernel - Re: [PATCH v2] exec: make de

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Date:   Wed, 14 Nov 2018 15:37:06 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Chanho Min <chanho.min@....com>,
        "'Rafael J. Wysocki'" <rjw@...ysocki.net>,
        'Pavel Machek' <pavel@....cz>,
        'Len Brown' <len.brown@...el.com>,
        'Andrew Morton' <akpm@...ux-foundation.org>,
        "'Eric W. Biederman'" <ebiederm@...ssion.com>,
        'Christian Brauner' <christian@...uner.io>,
        'Anna-Maria Gleixner' <anna-maria@...utronix.de>,
        'Alexander Viro' <viro@...iv.linux.org.uk>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        'Seungho Park' <seungho1.park@....com>,
        'Inkyu Hwang' <inkyu.hwang@....com>,
        'Donghwan Jung' <donghwan.jung@....com>,
        'Jongsung Kim' <neidhard.kim@....com>
Subject: Re: [PATCH v2] exec: make de_thread() freezable

On 11/14, Michal Hocko wrote:
>
> > I don't understand why it isn't appropriate for exec to block. The
> > exec can freeze. When tasks are thawed, the killed sub-thread will die
> > and wake de_thread(). The exec will continue to work from resume.
>
> Because this is fragile.

I don't really agree, but...

> I haven't checked the full set of resources the
> task holds when in this path but I can imagine we can introduce lock
> dependency on freezing really easily.

And you are right, see another email I sent you a minute ago.

But again, we need to change de_thread to sleep without cred_guard_mutex
anyway, so I think this change is fine. At least in that it can't add the
new problems.

Oleg.