linux-kernel - Re: [PATCH 1/4] gpio: Remove VLA from gpiolib

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Message-ID: <20180328035455.GA18149@wunner.de>
Date:   Wed, 28 Mar 2018 05:54:55 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Laura Abbott <labbott@...hat.com>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        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,
        Mathias Duckeck <m.duckeck@...bus.de>,
        Nandor Han <nandor.han@...com>,
        Semi Malinen <semi.malinen@...com>,
        Patrice Chotard <patrice.chotard@...com>
Subject: Re: [PATCH 1/4] gpio: Remove VLA from gpiolib

On Tue, Mar 27, 2018 at 05:37:18PM -0700, Laura Abbott wrote:
> On 03/18/2018 07:23 AM, Lukas Wunner wrote:
> > Actually, scratch that.  If ngpio is usually smallish, we can just
> > allocate reasonably sized space for mask and bits on the stack,
> > and fall back to the kcalloc slowpath only if chip->ngpio exceeds
> > that limit.  Basically the below (likewise compile-tested only),
> > this is on top of Laura's patch, could be squashed together.
> > Let me know what you think, thanks.
> >
> 
> It seems like there's general consensus this is okay so I'm going
> to fold it into the next version. If not, we can discuss again.

Yes, feel free to squash into your original patch with my S-o-b,
keep your authorship.

You may want to raise FASTPATH_NGPIO to something like 384, 448 or 512
to accommodate for the Intel chips Andy mentioned.  It's kind of a
"640k should be enough for everyone" thing but I'd expect the performance
impact of the extra bytes on the stack / memsetting them to zero
to be absolutely negligible.

Thanks!

Lukas