linux-kernel - Re: [RFC 5/7] mm: introduce external memory hinting API

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Message-ID: <20190527151201.GB8961@redhat.com>
Date:   Mon, 27 May 2019 17:12:02 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Tim Murray <timmurray@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Daniel Colascione <dancol@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Brian Geffon <bgeffon@...gle.com>
Subject: Re: [RFC 5/7] mm: introduce external memory hinting API

On 05/27, Minchan Kim wrote:
>
> > another problem is that pid_task(pid) can return a zombie leader, in this case
> > mm_access() will fail while it shouldn't.
>
> I'm sorry. I didn't notice that. However, I couldn't understand your point.
> Why do you think mm_access shouldn't fail even though pid_task returns
> a zombie leader?

The leader can exit (call sys_exit(), not sys_exit_group()), this won't affect
other threads. In this case the process is still alive even if the leader thread
is zombie. That is why we have find_lock_task_mm().

Oleg.