From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH 09/19] net: average: Kill off ACCESS_ONCE() Date: Tue, 24 Oct 2017 06:49:39 -0700 Message-ID: <20171024134939.GY3659@linux.vnet.ibm.com> References: <20171023210408.GA2930@linux.vnet.ibm.com> <1508792849-3115-9-git-send-email-paulmck@linux.vnet.ibm.com> <1508824691.2639.26.camel@sipsolutions.net> <20171024093412.slvps6vmluzmteru@gmail.com> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:40124 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751692AbdJXNtp (ORCPT ); Tue, 24 Oct 2017 09:49:45 -0400 Received: from pps.filterd (m0098417.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v9ODhHa3062386 for ; Tue, 24 Oct 2017 09:49:44 -0400 Received: from e17.ny.us.ibm.com (e17.ny.us.ibm.com [129.33.205.207]) by mx0a-001b2d01.pphosted.com with ESMTP id 2dt6jqs3f6-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Tue, 24 Oct 2017 09:49:44 -0400 Received: from localhost by e17.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 24 Oct 2017 09:49:43 -0400 Content-Disposition: inline In-Reply-To: <20171024093412.slvps6vmluzmteru@gmail.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Ingo Molnar Cc: Johannes Berg , "linux-kernel@vger.kernel.org" , "linux-arch@vger.kernel.org" , "will.deacon@arm.com" , "mark.rutland@arm.com" , "snitzer@redhat.com" , "thor.thayer@linux.intel.com" , "viro@zeniv.linux.org.uk" , "davem@davemloft.net" , "shuah@kernel.org" , "mpe@ellerman.id.au" , "tj@kernel.org" , "torvalds@linux-foundation.org" On Tue, Oct 24, 2017 at 11:34:13AM +0200, Ingo Molnar wrote: > > * Johannes Berg wrote: > > > On Mon, 2017-10-23 at 21:07 +0000, Paul E. McKenney wrote: > > > From: Mark Rutland > > > > > > For several reasons, it is desirable to use {READ,WRITE}_ONCE() in > > > preference to ACCESS_ONCE(), and new code is expected to use one of the > > > former. So far, there's been no reason to change most existing uses of > > > ACCESS_ONCE(), as these aren't currently harmful. > > > > > > However, for some features it is necessary to instrument reads and > > > writes separately, which is not possible with ACCESS_ONCE(). This > > > distinction is critical to correct operation. > > > > > > It's possible to transform the bulk of kernel code using the Coccinelle > > > script below. However, this doesn't pick up some uses, including those > > > in . As a preparatory step, this patch converts the > > > file to use {READ,WRITE}_ONCE() consistently. > > > > > > At the same time, this patch addds missing includes necessary for > > > {READ,WRITE}_ONCE(), *BUG_ON*(), and ilog2(). > > > > > > ---- > > > virtual patch > > > > > > @ depends on patch @ > > > expression E1, E2; > > > @@ > > > > > > - ACCESS_ONCE(E1) = E2 > > > + WRITE_ONCE(E1, E2) > > > > > > @ depends on patch @ > > > expression E; > > > @@ > > > > > > - ACCESS_ONCE(E) > > > + READ_ONCE(E) > > > ---- > > > > > > Signed-off-by: Mark Rutland > > > Cc: Johannes Berg > > > > Reviewed-by: Johannes Berg > > Thanks! > > > Let me know if you want me to apply this, since I seem to be the > > average.h maintainer :-) > > Would be nice to keep these patches together if possible, so that we can remove > ACCESS_ONCE() - or at least add a build warning. My goal is to remove it. After all, I am the guy who added it. ;-) Thanx, Paul