Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756026AbbGTNjK (ORCPT ); Mon, 20 Jul 2015 09:39:10 -0400 Received: from foss.arm.com ([217.140.101.70]:55809 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753230AbbGTNjI (ORCPT ); Mon, 20 Jul 2015 09:39:08 -0400 Date: Mon, 20 Jul 2015 14:39:06 +0100 From: Will Deacon To: Benjamin Herrenschmidt Cc: "paulmck@linux.vnet.ibm.com" , Michael Ellerman , "linux-arch@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Peter Zijlstra Subject: Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() Message-ID: <20150720133906.GG9908@arm.com> References: <1436826689.3948.233.camel@kernel.crashing.org> <1436929578.10956.3.camel@ellerman.id.au> <20150715104420.GD1005@arm.com> <1437012028.28475.2.camel@ellerman.id.au> <1437023004.28088.27.camel@kernel.crashing.org> <1437023695.28088.29.camel@kernel.crashing.org> <20150716151142.GR3717@linux.vnet.ibm.com> <1437087265.28088.53.camel@kernel.crashing.org> <20150717093221.GB18994@arm.com> <1437171254.28088.87.camel@kernel.crashing.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1437171254.28088.87.camel@kernel.crashing.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 864 Lines: 23 On Fri, Jul 17, 2015 at 11:14:14PM +0100, Benjamin Herrenschmidt wrote: > On Fri, 2015-07-17 at 10:32 +0100, Will Deacon wrote: > > static inline void arch_spin_unlock(arch_spinlock_t *lock) > > { > > - SYNC_IO; > > - __asm__ __volatile__("# arch_spin_unlock\n\t" > > - PPC_RELEASE_BARRIER: : :"memory"); > > + smp_mb(); > > lock->slock = 0; > > } > > That probably needs to be mb() in case somebody has the expectation that > it does a barrier vs. DMA on UP. Hmm, but on !SMP doesn't arch_spin_unlock effectively expand to barrier() in the core code? Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/