linux-kernel - Re: [PATCH 4/8] asm-generic: add atomic-instrumented.h

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Date:   Wed, 29 Mar 2017 14:27:18 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>, peterz@...radead.org,
        mingo@...hat.com, akpm@...ux-foundation.org, will.deacon@....com,
        aryabinin@...tuozzo.com, kasan-dev@...glegroups.com,
        linux-kernel@...r.kernel.org, x86@...nel.org, linux-mm@...ck.org
Subject: Re: [PATCH 4/8] asm-generic: add atomic-instrumented.h

On Tue, Mar 28, 2017 at 02:35:13PM -0700, Matthew Wilcox wrote:
> On Tue, Mar 28, 2017 at 06:15:41PM +0200, Dmitry Vyukov wrote:
> > The new header allows to wrap per-arch atomic operations
> > and add common functionality to all of them.
> 
> Why a new header instead of putting this in linux/atomic.h?

The idea was that doing it this way allowed architectures to switch over
to the arch_* naming without a flag day. Currently this only matters for
KASAN, which is only supported by a couple of architectures (arm64,
x86).

I seem to recall that there was an issue that prevented us from solving
this with ifdeffery early in linux/atomic.h like:

#ifdef arch_op
#define op(...) ({ 		\
	kasna_whatever(...)	\
	arch_op(...)		\
})
#endif

... but I can't recall specifically what it was.

Thanks,
Mark.