From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1751555AbbJTDqQ (ORCPT <rfc822;w@1wt.eu>);
	Mon, 19 Oct 2015 23:46:16 -0400
Received: from mx2.suse.de ([195.135.220.15]:49731 "EHLO mx2.suse.de"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1750868AbbJTDqP (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Mon, 19 Oct 2015 23:46:15 -0400
Date: Mon, 19 Oct 2015 20:46:02 -0700
From: Davidlohr Bueso <dave@stgolabs.net>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: Waiman Long <Waiman.Long@hpe.com>, Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, Scott J Norton <scott.norton@hpe.com>,
        Douglas Hatch <doug.hatch@hpe.com>
Subject: Re: [PATCH tip/locking/core v8 1/5] locking/qspinlock: Use
 _acquire/_release versions of cmpxchg & xchg
Message-ID: <20151020034602.GC27292@linux-uzut.site>
References: <1444949467-34807-1-git-send-email-Waiman.Long@hpe.com>
 <1444949467-34807-2-git-send-email-Waiman.Long@hpe.com>
 <20151020031714.GA935@fixme-laptop.cn.ibm.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha1;
	protocol="application/pgp-signature"; boundary="XsQoSWH+UP9D9v3l"
Content-Disposition: inline
In-Reply-To: <20151020031714.GA935@fixme-laptop.cn.ibm.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


--XsQoSWH+UP9D9v3l
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Disposition: inline

On Tue, 20 Oct 2015, Boqun Feng wrote:

>> @@ -93,7 +94,7 @@ static __always_inline void queued_spin_unlock(struct qspinlock *lock)
>>  	/*
>>  	 * smp_mb__before_atomic() in order to guarantee release semantics
>>  	 */
>> -	smp_mb__before_atomic_dec();
>> +	smp_mb__before_atomic();
>>  	atomic_sub(_Q_LOCKED_VAL, &lock->val);
>
>Just be curious, you don't use atomic_sub_release() here on purpose?

atomic_sub() does not imply barriers, so there's no relaxed variants; that's
only for _return() (and such) to the caller.

Thanks,
Davidlohr
--XsQoSWH+UP9D9v3l
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: Digital signature

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2
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=mUIl
-----END PGP SIGNATURE-----

--XsQoSWH+UP9D9v3l--