From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754730AbbKLOuJ (ORCPT ); Thu, 12 Nov 2015 09:50:09 -0500 Received: from unicorn.mansr.com ([81.2.72.234]:48103 "EHLO unicorn.mansr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753364AbbKLOuH convert rfc822-to-8bit (ORCPT ); Thu, 12 Nov 2015 09:50:07 -0500 From: =?iso-8859-1?Q?M=E5ns_Rullg=E5rd?= To: "Paul E. McKenney" Cc: Peter Zijlstra , ralf@linux-mips.org, ddaney@caviumnetworks.com, linux-kernel@vger.kernel.org, Will Deacon , torvalds@linux-foundation.org, boqun.feng@gmail.com Subject: Re: [RFC][PATCH] mips: Fix arch_spin_unlock() References: <20151112123123.GZ17308@twins.programming.kicks-ass.net> <20151112143231.GS3972@linux.vnet.ibm.com> Date: Thu, 12 Nov 2015 14:50:00 +0000 In-Reply-To: <20151112143231.GS3972@linux.vnet.ibm.com> (Paul E. McKenney's message of "Thu, 12 Nov 2015 06:32:31 -0800") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org "Paul E. McKenney" writes: > On Thu, Nov 12, 2015 at 01:31:23PM +0100, Peter Zijlstra wrote: >> Hi >> >> I think the MIPS arch_spin_unlock() is borken. >> >> spin_unlock() must have RELEASE semantics, these require that no LOADs >> nor STOREs leak out from the critical section. >> >> >From what I know MIPS has a relaxed memory model which allows reads to >> pass stores, and as implemented arch_spin_unlock() only issues a wmb >> which doesn't order prior reads vs later stores. >> >> Therefore upgrade the wmb() to smp_mb(). >> >> (Also, why the unconditional wmb, as opposed to smp_wmb() ?) > > One guess is that they want to order I/O accesses within the critical > section? Isn't that what mmiowb() is for? >> Maybe-Signed-off-by: Peter Zijlstra (Intel) >> --- >> diff --git a/arch/mips/include/asm/spinlock.h b/arch/mips/include/asm/spinlock.h >> index 40196bebe849..b2ca13f06152 100644 >> --- a/arch/mips/include/asm/spinlock.h >> +++ b/arch/mips/include/asm/spinlock.h >> @@ -140,7 +140,7 @@ static inline void arch_spin_lock(arch_spinlock_t *lock) >> static inline void arch_spin_unlock(arch_spinlock_t *lock) >> { >> unsigned int serving_now = lock->h.serving_now + 1; >> - wmb(); >> + smp_mb(); >> lock->h.serving_now = (u16)serving_now; >> nudge_writes(); >> } >> > -- Måns Rullgård mans@mansr.com