linux-kernel - Re: [PATCH] userfaultfd: hugetlbfs: add UFFDIO

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Date:   Fri, 17 Feb 2017 21:51:24 +0100
From:   Andrea Arcangeli <aarcange@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Hillf Danton <hillf.zj@...baba-inc.com>,
        Pavel Emelyanov <xemul@...allels.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>
Subject: Re: [PATCH] userfaultfd: hugetlbfs: add UFFDIO_COPY support for
 shared mappings

On Fri, Feb 17, 2017 at 12:17:38PM -0800, Andrew Morton wrote:
> I merged this up and a small issue remains:

Great!

> The value of `err' here is EINVAL.  That sems appropriate, but it only
> happens by sheer luck.

It might have been programmer luck but just for completeness, at
runtime no luck was needed (the temporary setting to ENOENT is undoed
before the if clause is closed). Your addition is surely safer just in
case of future changes missing how we inherited the EINVAL in both
branches, thanks! (plus the compiler should be able to optimize it
away until after it will be needed)