From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH RFC memory-model 0/6] LKMM updates Date: Thu, 10 Jan 2019 06:31:37 -0800 Message-ID: <20190110143137.GJ1215@linux.ibm.com> References: <20190109210706.GA27268@linux.ibm.com> <20190109231852.GA4494@andrea> <20190109234043.GD1215@linux.ibm.com> <20190110003952.GA4354@andrea> <20190110042027.GG1215@linux.ibm.com> <20190110084024.GA10280@andrea> Reply-To: paulmck@linux.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20190110084024.GA10280@andrea> Sender: linux-kernel-owner@vger.kernel.org To: Andrea Parri Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, mingo@kernel.org, stern@rowland.harvard.edu, parri.andrea@gmail.com, will.deacon@arm.com, peterz@infradead.org, boqun.feng@gmail.com, npiggin@gmail.com, dhowells@redhat.com, j.alglave@ucl.ac.uk, luc.maranget@inria.fr, akiyks@gmail.com, willy@infradead.org List-Id: linux-arch.vger.kernel.org On Thu, Jan 10, 2019 at 09:40:24AM +0100, Andrea Parri wrote: > > > > > It seems that > > > > > > > > > > 1b52d0186177 ("tools/memory-model: Model smp_mb__after_unlock_lock()") > > > > > > > > > > from linux-rcu/dev got lost; this also needs an ack (probably yours! ;D, > > > > > considered that, IIRC, you introduced the primitive and RCU is currently > > > > > its only user.) > > > > > > > > That commit is in -tip: > > > > > > > > 4607abbcf464 ("tools/memory-model: Model smp_mb__after_unlock_lock()") > > > > > > > > So it has already left my -rcu tree. ;-) > > > > > > Oh, you're right: now I see the commit (e.g., with "git show"), but I > > > don't see the corresponding changes applied to the tree. > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=locking/core&id=4607abbcf464ea2be14da444215d05c73025cf6e > > > https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/tree/tools/memory-model/linux-kernel.bell?h=locking/core > > > > > > Is this expected? > > > > Are you asking why it is in -tip but not in mainline? I am not sure, > > but given that the merge window was over the holiday season and that > > the length of the merge window proved to be shorter than many people > > expected it to be, I am not too surprised. ;-) > > Mmh, let me try again: > > $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git > $ cd tip > $ git checkout -b locking/core origin/locking/core > > $ git show 4607abbcf464 > commit 4607abbcf464ea2be14da444215d05c73025cf6e > Author: Andrea Parri > Date: Mon Dec 3 15:04:49 2018 -0800 > > tools/memory-model: Model smp_mb__after_unlock_lock() > > $ cd tools/memory-model > $ herd7 -conf linux-kernel.cfg after-unlock-lock-same-cpu.litmus > File "after-unlock-lock-same-cpu.litmus": Unknown macro smp_mb__after_unlock_lock (User error) > > [aka, linux-kernel.def in tip:locking/core does not have the > smp_mb__after_unlock_lock() added by 4607abbcf464] Color me confused: ------------------------------------------------------------------------ $ git checkout 4607abbcf464Checking out files: 100% (18397/18397), done. Previous HEAD position was 4e284b1bf15a rcu: Remove wrapper definitions for obsolete RCU update functions HEAD is now at 4607abbcf464 tools/memory-model: Model smp_mb__after_unlock_lock() $ grep smp_mb__after_unlock_lock tools/memory-model/linux-kernel.def smp_mb__after_unlock_lock() { __fence{after-unlock-lock}; } ------------------------------------------------------------------------ In addition, it handles this litmus test just fine: ------------------------------------------------------------------------ C MP+polocks (* * Result: Never * * This litmus test demonstrates how lock acquisitions and releases can * stand in for smp_load_acquire() and smp_store_release(), respectively. * In other words, when holding a given lock (or indeed after releasing a * given lock), a CPU is not only guaranteed to see the accesses that other * CPUs made while previously holding that lock, it is also guaranteed * to see all prior accesses by those other CPUs. *) {} P0(int *x, int *y, spinlock_t *mylock) { WRITE_ONCE(*x, 1); spin_lock(mylock); smp_mb__after_unlock_lock(); WRITE_ONCE(*y, 1); spin_unlock(mylock); } P1(int *x, int *y, spinlock_t *mylock) { int r0; int r1; spin_lock(mylock); r0 = READ_ONCE(*y); spin_unlock(mylock); r1 = READ_ONCE(*x); } exists (1:r0=1 /\ 1:r1=0) ------------------------------------------------------------------------ Again, color me confused. Thanx, Paul From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:39424 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728191AbfAJObq (ORCPT ); Thu, 10 Jan 2019 09:31:46 -0500 Received: from pps.filterd (m0098396.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id x0AET9iG125164 for ; Thu, 10 Jan 2019 09:31:45 -0500 Received: from e16.ny.us.ibm.com (e16.ny.us.ibm.com [129.33.205.206]) by mx0a-001b2d01.pphosted.com with ESMTP id 2px5w5x9jv-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 10 Jan 2019 09:31:44 -0500 Received: from localhost by e16.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 10 Jan 2019 14:31:43 -0000 Date: Thu, 10 Jan 2019 06:31:37 -0800 From: "Paul E. McKenney" Subject: Re: [PATCH RFC memory-model 0/6] LKMM updates Reply-To: paulmck@linux.ibm.com References: <20190109210706.GA27268@linux.ibm.com> <20190109231852.GA4494@andrea> <20190109234043.GD1215@linux.ibm.com> <20190110003952.GA4354@andrea> <20190110042027.GG1215@linux.ibm.com> <20190110084024.GA10280@andrea> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190110084024.GA10280@andrea> Message-ID: <20190110143137.GJ1215@linux.ibm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Andrea Parri Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, mingo@kernel.org, stern@rowland.harvard.edu, parri.andrea@gmail.com, will.deacon@arm.com, peterz@infradead.org, boqun.feng@gmail.com, npiggin@gmail.com, dhowells@redhat.com, j.alglave@ucl.ac.uk, luc.maranget@inria.fr, akiyks@gmail.com, willy@infradead.org Message-ID: <20190110143137.fWFUliYfEalccbyQnhzMCbAR-GRuS7djPhfFsFBK1ds@z> On Thu, Jan 10, 2019 at 09:40:24AM +0100, Andrea Parri wrote: > > > > > It seems that > > > > > > > > > > 1b52d0186177 ("tools/memory-model: Model smp_mb__after_unlock_lock()") > > > > > > > > > > from linux-rcu/dev got lost; this also needs an ack (probably yours! ;D, > > > > > considered that, IIRC, you introduced the primitive and RCU is currently > > > > > its only user.) > > > > > > > > That commit is in -tip: > > > > > > > > 4607abbcf464 ("tools/memory-model: Model smp_mb__after_unlock_lock()") > > > > > > > > So it has already left my -rcu tree. ;-) > > > > > > Oh, you're right: now I see the commit (e.g., with "git show"), but I > > > don't see the corresponding changes applied to the tree. > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=locking/core&id=4607abbcf464ea2be14da444215d05c73025cf6e > > > https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/tree/tools/memory-model/linux-kernel.bell?h=locking/core > > > > > > Is this expected? > > > > Are you asking why it is in -tip but not in mainline? I am not sure, > > but given that the merge window was over the holiday season and that > > the length of the merge window proved to be shorter than many people > > expected it to be, I am not too surprised. ;-) > > Mmh, let me try again: > > $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git > $ cd tip > $ git checkout -b locking/core origin/locking/core > > $ git show 4607abbcf464 > commit 4607abbcf464ea2be14da444215d05c73025cf6e > Author: Andrea Parri > Date: Mon Dec 3 15:04:49 2018 -0800 > > tools/memory-model: Model smp_mb__after_unlock_lock() > > $ cd tools/memory-model > $ herd7 -conf linux-kernel.cfg after-unlock-lock-same-cpu.litmus > File "after-unlock-lock-same-cpu.litmus": Unknown macro smp_mb__after_unlock_lock (User error) > > [aka, linux-kernel.def in tip:locking/core does not have the > smp_mb__after_unlock_lock() added by 4607abbcf464] Color me confused: ------------------------------------------------------------------------ $ git checkout 4607abbcf464Checking out files: 100% (18397/18397), done. Previous HEAD position was 4e284b1bf15a rcu: Remove wrapper definitions for obsolete RCU update functions HEAD is now at 4607abbcf464 tools/memory-model: Model smp_mb__after_unlock_lock() $ grep smp_mb__after_unlock_lock tools/memory-model/linux-kernel.def smp_mb__after_unlock_lock() { __fence{after-unlock-lock}; } ------------------------------------------------------------------------ In addition, it handles this litmus test just fine: ------------------------------------------------------------------------ C MP+polocks (* * Result: Never * * This litmus test demonstrates how lock acquisitions and releases can * stand in for smp_load_acquire() and smp_store_release(), respectively. * In other words, when holding a given lock (or indeed after releasing a * given lock), a CPU is not only guaranteed to see the accesses that other * CPUs made while previously holding that lock, it is also guaranteed * to see all prior accesses by those other CPUs. *) {} P0(int *x, int *y, spinlock_t *mylock) { WRITE_ONCE(*x, 1); spin_lock(mylock); smp_mb__after_unlock_lock(); WRITE_ONCE(*y, 1); spin_unlock(mylock); } P1(int *x, int *y, spinlock_t *mylock) { int r0; int r1; spin_lock(mylock); r0 = READ_ONCE(*y); spin_unlock(mylock); r1 = READ_ONCE(*x); } exists (1:r0=1 /\ 1:r1=0) ------------------------------------------------------------------------ Again, color me confused. Thanx, Paul