linux-kernel - Re: [PATCH] userfaultfd_zeropage: return -ENOSPC in case mm has gone

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Message-ID: <20170802164001.GF21775@redhat.com>
Date:   Wed, 2 Aug 2017 18:40:01 +0200
From:   Andrea Arcangeli <aarcange@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        linux-mm <linux-mm@...ck.org>,
        lkml <linux-kernel@...r.kernel.org>, stable@...r.kernel.org
Subject: Re: [PATCH] userfaultfd_zeropage: return -ENOSPC in case mm has gone

On Wed, Aug 02, 2017 at 06:22:49PM +0200, Michal Hocko wrote:
> ESRCH refers to "no such process". Strictly speaking userfaultfd code is
> about a mm which is gone but that is a mere detail. In fact the owner of

Well this whole issue about which retval, is about a mere detail in
the first place, so I don't think you can discount all other mere
details as irrelevant in the evaluation of a change to solve a mere
detail.

> But as I've said, this might be really risky to change. My impression
> was that userfaultfd is not widely used yet and those can be fixed
> easily but if that is not the case then we have to live with the current
> ENOSPC.

The only change would be for userfaultfd non cooperative mode, and
CRIU is the main user of that. So I think it is up to Mike to decide,
I'm fine either ways. I certainly agree ESRCH could be a slightly
better fit, I only wanted to clarify it's not a 100% match either.