linux-kernel - Re: [PATCH 03/16] mm: simplify gup_fast

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Message-ID: <CAHk-=wg5mww3StP8HqPN4d5eij3KmEayM743v-nDKAMgRe2J6g@mail.gmail.com>
Date:   Mon, 3 Jun 2019 09:08:43 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>,
        Nicholas Piggin <npiggin@...il.com>,
        Khalid Aziz <khalid.aziz@...cle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-mips@...r.kernel.org,
        Linux-sh list <linux-sh@...r.kernel.org>,
        sparclinux@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Linux-MM <linux-mm@...ck.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 03/16] mm: simplify gup_fast_permitted

On Mon, Jun 3, 2019 at 12:41 AM Christoph Hellwig <hch@....de> wrote:
>
> I only removed a duplicate of it.

I don't see any remaining cases.

> The full (old) code in get_user_pages_fast() looks like this:
>
>         if (nr_pages <= 0)
>                 return 0;
>
>         if (unlikely(!access_ok((void __user *)start, len)))
>                 return -EFAULT;
>
>         if (gup_fast_permitted(start, nr_pages)) {

Yes, and that code was correct.

The new code has no test at all for "nr_pages == 0", afaik.

                 Linus