From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH 09/19] net: average: Kill off ACCESS_ONCE() Date: Tue, 24 Oct 2017 11:34:13 +0200 Message-ID: <20171024093412.slvps6vmluzmteru@gmail.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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1508824691.2639.26.camel@sipsolutions.net> Sender: linux-kernel-owner@vger.kernel.org To: Johannes Berg Cc: "Paul E. McKenney" , "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" List-Id: linux-arch.vger.kernel.org * 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. Thanks, Ingo From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f65.google.com ([74.125.82.65]:55609 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751874AbdJXJeR (ORCPT ); Tue, 24 Oct 2017 05:34:17 -0400 Date: Tue, 24 Oct 2017 11:34:13 +0200 From: Ingo Molnar Subject: Re: [PATCH 09/19] net: average: Kill off ACCESS_ONCE() Message-ID: <20171024093412.slvps6vmluzmteru@gmail.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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1508824691.2639.26.camel@sipsolutions.net> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Johannes Berg Cc: "Paul E. McKenney" , "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" Message-ID: <20171024093413.RIKSpP1d2gjrUkBuD4z-wQyJspYpPiFUhbTv-Mjv2jc@z> * 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. Thanks, Ingo