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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Thu, 10 Jan 2019 14:31:37 -0000 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22033.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x0AEVaid26673222 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Thu, 10 Jan 2019 14:31:36 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C08E3B2064; Thu, 10 Jan 2019 14:31:36 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 8EA7EB205F; Thu, 10 Jan 2019 14:31:36 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.88]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Thu, 10 Jan 2019 14:31:36 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 4A02E16C5FAB; Thu, 10 Jan 2019 06:31:37 -0800 (PST) Date: Thu, 10 Jan 2019 06:31:37 -0800 From: "Paul E. McKenney" 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 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> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 19011014-0072-0000-0000-000003E7DE05 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00010379; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000274; SDB=6.01144478; UDB=6.00595910; IPR=6.00924742; MB=3.00025068; MTD=3.00000008; XFM=3.00000015; UTC=2019-01-10 14:31:42 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19011014-0073-0000-0000-00004AC1F1E3 Message-Id: <20190110143137.GJ1215@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-01-10_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1901100115 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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