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

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Date:   Thu, 29 Mar 2018 16:25:33 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Laura Abbott <labbott@...hat.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Kees Cook <keescook@...omium.org>, linux-gpio@...r.kernel.org,
        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 11:18:09AM -0700, Laura Abbott 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.
> 
> Signed-off-by: Lukas Wunner <lukas@...ner.de>
> Signed-off-by: Laura Abbott <labbott@...hat.com>
> ---
> v3: Split out from the series since patches have been picked up
> independently. Fold in patch from Lukas Wunner to introduce slow/fast
> paths. I took his suggestions to go with 384 as the maximum number of
> gpios. Also fixed one 0-day bot issue where I forgot to change the
> return type.

I've just given this a whirl with gpio-hammer and it works nicely, so FWIW:

Reviewed-and-tested-by: Lukas Wunner <lukas@...ner.de>

Thanks a lot for doing this Laura, and most of all thanks for the
proverbial "dogged persistence and patience"!
(https://lwn.net/Articles/697029/)

Lukas