Re: [PATCHv3] gpio: Remove VLA from gpiolib

[Laura Abbott]

On 03/30/2018 07:33 AM, Andy Shevchenko wrote:
> On Wed, Mar 28, 2018 at 9:18 PM, Laura Abbott <labbott@xxxxxxxxxx> wrote:
> > The new challenge is to remove VLAs from the kernel
> > (see https://lkml.org/lkml/2018/3/7/621) to eventually
> > turn on -Wvla.
> >
> > Using a kmalloc array is the easy way to fix this but kmalloc is still
> > more expensive than stack allocation. Introduce a fast path with a
> > fixed size stack array to cover most chip with gpios below some fixed
> > amount. The slow path dynamically allocates an array to cover those
> > chips with a large number of gpios.
>
> > +               ret = gpiod_set_array_value_complex(false,
> >                                                true,
> >                                                lh->numdescs,
> >                                                lh->descs,
> >                                                vals);
> > +               if (ret)
> > +                       return ret;
> > +
> >                  return 0;
>
> Can't we
>
> return gpiod_set_array_value_complex(); ?

Yeah I'll clean that up for v4.

> > +                       slowpath = kcalloc(2 * BITS_TO_LONGS(chip->ngpio),
> > +                                          sizeof(*slowpath),
> > +                                          can_sleep ? GFP_KERNEL : GFP_ATOMIC);
>
>
> > +                       if (slowpath)
> > +                               kfree(slowpath);
>
> > +               if (slowpath)
> > +                       kfree(slowpath);
>
> Since slowpath is a pointer, conditionals above are redundant.
>
> > +                       slowpath = kcalloc(2 * BITS_TO_LONGS(chip->ngpio),
> > +                                          sizeof(*slowpath),
> > +                                          can_sleep ? GFP_KERNEL : GFP_ATOMIC);
>
> > +               if (slowpath)
> > +                       kfree(slowpath);
>
> Ditto.

This was caught by a coccinelle script via 0-day but I think the request
was to not do it. I'll add a comment explaining why we are going against
style.

Thanks,
Laura