linux-kernel - Re: [PATCH v2 18/20] kasan: clean up metadata allocation and usage

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Date:   Thu, 12 Nov 2020 21:11:43 +0100
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Marco Elver <elver@...gle.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 18/20] kasan: clean up metadata allocation and usage

On Thu, Nov 12, 2020 at 12:06 AM Marco Elver <elver@...gle.com> wrote:
>
> > +     /* Limit it with KMALLOC_MAX_SIZE (relevant for SLAB only). */
> > +     if (optimal_size > KMALLOC_MAX_SIZE)
> > +             optimal_size = KMALLOC_MAX_SIZE;
> > +     /* Use optimal size if the size with added metas is not large enough. */
>
> Uses the optimal size if it's not "too large" rather than "not large
> enough", right?

Not really. If the redzone composed from metas is begger than optimal
redzone - we're good. If it's not large enough to reach optimal
redzone - we need to make it bigger.

> As it is worded now makes me think this is a fallback,
> whereas ideally it's the common case, right?

It's hard to say which case is more common, as optimal redzone size
varies and depends on the object size.

[...]

Will fix the rest of the comments, thanks!