Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 23 May 2019 10:30:13 +0200
From:   Andrea Parri <andrea.parri@amarulasolutions.com>
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     linux-kernel@vger.kernel.org, peterz@infradead.org,
        will.deacon@arm.com, aou@eecs.berkeley.edu, arnd@arndb.de,
        bp@alien8.de, catalin.marinas@arm.com, davem@davemloft.net,
        fenghua.yu@intel.com, heiko.carstens@de.ibm.com,
        herbert@gondor.apana.org.au, ink@jurassic.park.msu.ru,
        jhogan@kernel.org, linux@armlinux.org.uk, mattst88@gmail.com,
        mingo@kernel.org, mpe@ellerman.id.au, palmer@sifive.com,
        paul.burton@mips.com, paulus@samba.org, ralf@linux-mips.org,
        rth@twiddle.net, stable@vger.kernel.org, tglx@linutronix.de,
        tony.luck@intel.com, vgupta@synopsys.com
Subject: Re: [PATCH 00/18] locking/atomic: atomic64 type cleanup
Message-ID: <20190523083013.GA4616@andrea>
References: <20190522132250.26499-1-mark.rutland@arm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20190522132250.26499-1-mark.rutland@arm.com>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hi Mark,

On Wed, May 22, 2019 at 02:22:32PM +0100, Mark Rutland wrote:
> Currently architectures return inconsistent types for atomic64 ops. Some return
> long (e..g. powerpc), some return long long (e.g. arc), and some return s64
> (e.g. x86).

(only partially related, but probably worth asking:)

While reading the series, I realized that the following expression:

	atomic64_t v;
        ...
	typeof(v.counter) my_val = atomic64_set(&v, VAL);

is a valid expression on some architectures (in part., on architectures
which #define atomic64_set() to WRITE_ONCE()) but is invalid on others.
(This is due to the fact that WRITE_ONCE() can be used as an rvalue in
the above assignment; TBH, I ignore the reasons for having such rvalue?)

IIUC, similar considerations hold for atomic_set().

The question is whether this is a known/"expected" inconsistency in the
implementation of atomic64_set() or if this would also need to be fixed
/addressed (say in a different patchset)?

Thanks,
  Andrea