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Date: Sun, 8 Apr 2018 06:12:13 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [PATCH v2 1/3] mm/gup_benchmark: handle gup failures
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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>, Andrew Morton <akpm@linux-foundation.org>, Huang Ying <ying.huang@intel.com>, Jonathan Corbet <corbet@lwn.net>, Peter Zijlstra <peterz@infradead.org>, Thomas Gleixner <tglx@linutronix.de>, Thorsten Leemhuis <regressions@leemhuis.info>, stable <stable@vger.kernel.org>, linux-mm <linux-mm@kvack.org>

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@redhat.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;