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From: Dmitry Vyukov <dvyukov@google.com>
Date: Tue, 14 Mar 2017 20:25:32 +0100
Message-ID: <CACT4Y+Zx-fT+FSWm9B8=E9GH6KLoAL0ATDcU9MbBkwBC9+5qqQ@mail.gmail.com>
Subject: Re: [PATCH] x86, kasan: add KASAN checks to atomic operations
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To: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Will Deacon <will.deacon@arm.com>, Andrew Morton <akpm@linux-foundation.org>, Andrey Ryabinin <aryabinin@virtuozzo.com>, Ingo Molnar <mingo@redhat.com>, kasan-dev <kasan-dev@googlegroups.com>, "linux-mm@kvack.org" <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>, "x86@kernel.org" <x86@kernel.org>

On Tue, Mar 14, 2017 at 4:44 PM, Mark Rutland <mark.rutland@arm.com> 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.


Reverted xchg changes.
Added comments re READ_ONCE_NOCHECK() and WRITE_ONCE().
Added file comment.
Split into 3 patches and mailed.

Thanks!

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