linux-kernel - Re: [PATCH 1/3] asm-generic/atomic64: Add support for ARCH

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Message-Id: <1605491118.ek4lw8ppgq.astroid@bobo.none>
Date:   Mon, 16 Nov 2020 11:48:58 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Alexey Kardashevskiy <aik@...abs.ru>,
        Arnd Bergmann <arnd@...db.de>,
        Boqun Feng <boqun.feng@...il.com>,
        Christophe Leroy <christophe.leroy@....fr>,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH 1/3] asm-generic/atomic64: Add support for ARCH_ATOMIC

Excerpts from Peter Zijlstra's message of November 11, 2020 11:44 pm:
> On Wed, Nov 11, 2020 at 02:39:01PM +0100, Christophe Leroy wrote:
>> Hello,
>> 
>> Le 11/11/2020 à 12:07, Nicholas Piggin a écrit :
>> > This passes atomic64 selftest on ppc32 on qemu (uniprocessor only)
>> > both before and after powerpc is converted to use ARCH_ATOMIC.
>> 
>> Can you explain what this change does and why it is needed ?
> 
> That certainly should've been in the Changelog. This enables atomic
> instrumentation, see asm-generic/atomic-instrumented.h. IOW, it makes
> atomic ops visible to K*SAN.
> 

Right. This specific patch doesn't actually "do" anything except
allow generic atomic64 to be used with ARCH_ATOMIC. It does that
by re-naming some things to avoid name collisions and also providing
the arch_ prefix that ARCH_ATOMIC expects.

I don't know what should be in the changelog. I suppose the latter,
the former is discoverable by looking at ARCH_ATOMIC code and
patches but I guess it's polite and doesn't hurt to include the
former as well.

I'll send an update before long.

Thanks,
Nick