linux-kernel - Re: [PATCH v2 1/3] mm/gup_benchmark: handle gup failures

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Message-ID: <20180408060935-mutt-send-email-mst@kernel.org>
Date:   Sun, 8 Apr 2018 06:12:13 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Huang Ying <ying.huang@...el.com>,
        Jonathan Corbet <corbet@....net>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        stable <stable@...r.kernel.org>, linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH v2 1/3] mm/gup_benchmark: handle gup failures

On Sat, Apr 07, 2018 at 01:08:43PM -0700, Linus Torvalds wrote:
> On Thu, Apr 5, 2018 at 2:03 PM, Michael S. Tsirkin <mst@...hat.com> wrote:
> >
> >                 nr = get_user_pages_fast(addr, nr, gup->flags & 1, pages + i);
> > -               i += nr;
> > +               if (nr > 0)
> > +                       i += nr;
> 
> Can we just make this robust while at it, and just make it
> 
>         if (nr <= 0)
>                 break;
> 
> instead? Then it doesn't care about zero vs negative error, and
> wouldn't get stuck in an endless loop if it got zero.
> 
>              Linus

I don't mind though it alredy breaks out on the next cycle:

                if (nr != gup->nr_pages_per_call)
                        break;

the only issue is i getting corrupted when nr < 0;