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

[Andrew Morton]

On Sun, 8 Apr 2018 06:12:13 +0300 "Michael S. Tsirkin"  wrote:

> 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  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;
> 

It does help readability to have the thing bail out as soon as we see
something go bad.  This?

--- a/mm/gup_benchmark.c~mm-gup_benchmark-handle-gup-failures-fix
+++ a/mm/gup_benchmark.c
@@ -41,8 +41,9 @@ static int __gup_benchmark_ioctl(unsigne
}
 
nr = get_user_pages_fast(addr, nr, gup->flags & 1, pages + i);
-   if (nr > 0)
-   i += nr;
+   if (nr <= 0)
+   break;
+   i += nr;
}
end_time = ktime_get();
 
_

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

[Michael S. Tsirkin]

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  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;

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

[Linus Torvalds]

On Thu, Apr 5, 2018 at 2:03 PM, Michael S. Tsirkin  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