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Date: Fri, 18 May 2018 23:07:04 +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>, Rasmus Villemoes <linux@...musvillemoes.dk>,
"open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, kernel-hardening@...ts.openwall.com,
Phil Reid <preid@...ctromag.com.au>, Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCHv8] gpio: Remove VLA from gpiolib
On Fri, May 18, 2018 at 8:53 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.
> + unsigned long fastpath[2 * BITS_TO_LONGS(FASTPATH_NGPIO)];
> + unsigned long *mask, *bits;
> int first, j, ret;
>
> + if (likely(chip->ngpio <= FASTPATH_NGPIO)) {
> + mask = fastpath;
> + } else {
> + mask = kmalloc_array(2 * BITS_TO_LONGS(chip->ngpio),
> + sizeof(*mask),
> + can_sleep ? GFP_KERNEL : GFP_ATOMIC);
> + if (!mask)
> + return -ENOMEM;
> + }
> +
> + bits = mask + BITS_TO_LONGS(chip->ngpio);
> + memset(mask, 0, BITS_TO_LONGS(chip->ngpio) * sizeof(*mask));
Wouldn't be better
bitmap_zero(mask, chip->ngpio);
?
> + bits = mask + BITS_TO_LONGS(chip->ngpio);
> + memset(mask, 0, BITS_TO_LONGS(chip->ngpio) * sizeof(*mask));
Ditto.
--
With Best Regards,
Andy Shevchenko
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