linux-kernel - Re: [PATCH] x86, kasan: add KASAN checks to atomic operations

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Message-ID: <20170314154429.GB15740@leverpostej>
Date:   Tue, 14 Mar 2017 15:44:30 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Will Deacon <will.deacon@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Ingo Molnar <mingo@...hat.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH] x86, kasan: add KASAN checks to atomic operations

On Tue, Mar 14, 2017 at 04:32:30PM +0100, Peter Zijlstra wrote:
> On Tue, Mar 14, 2017 at 04:22:52PM +0100, Dmitry Vyukov wrote:
> > -static __always_inline int atomic_read(const atomic_t *v)
> > +static __always_inline int arch_atomic_read(const atomic_t *v)
> >  {
> > -	return READ_ONCE((v)->counter);
> > +	return READ_ONCE_NOCHECK((v)->counter);
> 
> Should NOCHEKC come with a comment, because i've no idea why this is so.

I suspect the idea is that given the wrapper will have done the KASAN
check, duplicating it here is either sub-optimal, or results in
duplicate splats. READ_ONCE() has an implicit KASAN check,
READ_ONCE_NOCHECK() does not.

If this is to solve duplicate splats, it'd be worth having a
WRITE_ONCE_NOCHECK() for arch_atomic_set().

Agreed on the comment, regardless.

Thanks,
Mark.