linux-kernel - Re: [PATCHv3] gpio: Remove VLA from gpiolib

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Date:   Fri, 30 Mar 2018 17:33:55 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Laura Abbott <labbott@...hat.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Kees Cook <keescook@...omium.org>,
        Lukas Wunner <lukas@...ner.de>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kernel-hardening@...ts.openwall.com,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCHv3] gpio: Remove VLA from gpiolib

On Wed, Mar 28, 2018 at 9:18 PM, Laura Abbott <labbott@...hat.com> 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(); ?


> +                       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.

-- 
With Best Regards,
Andy Shevchenko