From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S938209AbeBURxK (ORCPT ); Wed, 21 Feb 2018 12:53:10 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:50716 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S935104AbeBURxG (ORCPT ); Wed, 21 Feb 2018 12:53:06 -0500 Date: Wed, 21 Feb 2018 09:53:21 -0800 From: "Paul E. McKenney" To: Alan Stern Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, mingo@kernel.org, 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, nborisov@suse.com Subject: Re: [PATCH RFC tools/lkmm 10/12] tools/memory-model: Add a S lock-based external-view litmus test Reply-To: paulmck@linux.vnet.ibm.com References: <20180221161223.GE3617@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18022117-0048-0000-0000-0000023CFB83 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008570; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000254; SDB=6.00993054; UDB=6.00504563; IPR=6.00772398; MB=3.00019675; MTD=3.00000008; XFM=3.00000015; UTC=2018-02-21 17:53:01 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18022117-0049-0000-0000-000044354AB9 Message-Id: <20180221175320.GI3617@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-02-21_06:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 lowpriorityscore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1802210216 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 21, 2018 at 11:50:31AM -0500, Alan Stern wrote: > On Wed, 21 Feb 2018, Paul E. McKenney wrote: > > > On Wed, Feb 21, 2018 at 10:09:00AM -0500, Alan Stern wrote: > > > On Tue, 20 Feb 2018, Paul E. McKenney wrote: > > > > > > > From: Alan Stern > > > > > > > > This commit adds a litmus test in which P0() and P1() form a lock-based S > > > > litmus test, with the addition of P2(), which observes P0()'s and P1()'s > > > > > > Why do you call this an "S" litmus test? Isn't ISA2 a better > > > description? > > > > Indeed, the name of the test is in fact ISA2. > > Sure; and the Changelog entry should reflect this. No argument. > > > > accesses with a full memory barrier but without the lock. This litmus > > > > test asks whether writes carried out by two different processes under the > > > > same lock will be seen in order by a third process not holding that lock. > > > > The answer to this question is "yes" for all architectures supporting > > > > the Linux kernel, but is "no" according to the current version of LKMM. > > > > > > > > A patch to LKMM is under development. > > > > > > > > Signed-off-by: Alan Stern > > > > Signed-off-by: Paul E. McKenney > > > > --- > > > > .../ISA2+pooncelock+pooncelock+pombonce.litmus | 41 ++++++++++++++++++++++ > > > > 1 file changed, 41 insertions(+) > > > > create mode 100644 tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus > > > > > > Aren't these tests supposed to be described in litmus-tests/README? > > You apparently missed this recommendation. I did, please accept my apologies and please see below. > > > > diff --git a/tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus b/tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus > > > > new file mode 100644 > > > > index 000000000000..7a39a0aaa976 > > > > --- /dev/null > > > > +++ b/tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus > > > > @@ -0,0 +1,41 @@ > > > > +C ISA2+pooncelock+pooncelock+pombonce.litmus > > > > + > > > > +(* > > > > + * Result: Sometimes > > > > + * > > > > + * This test shows that the ordering provided by a lock-protected S > > > > + * litmus test (P0() and P1()) are not visible to external process P2(). > > > > + * This is likely to change soon. > > > > > > That last line may be premature. We haven't reached any consensus on > > > how RISC-V will handle this. If RISC-V allows the test then the memory > > > model can't forbid it. > > > > Agreed. How about this? If the RISC-V question is answered by the > > end of next week, I update accordingly. If not, I update the comment > > to give the details. > > The README also should be updated. Agreed. > > Hey, at least having the memory model go in at about the same time as > > a new architecture is giving us good practice! ;-) > > Hopefully things will settle down in a week or two. Here is hoping! Thanx, Paul ------------------------------------------------------------------------ commit e6658d1d7fcc6391f3d00beaadc484243123a893 Author: Paul E. McKenney Date: Wed Feb 21 09:49:01 2018 -0800 tools/memory-order: Add documentation of new litmus test The litmus-tests/README file lacked any mention of then litmus test named ISA2+pooncelock+pooncelock+pombonce.litmus. This commit therefore adds this test. Reported-by: Alan Stern Signed-off-by: Paul E. McKenney diff --git a/tools/memory-model/litmus-tests/README b/tools/memory-model/litmus-tests/README index dca7d823ad57..aff3eb90e067 100644 --- a/tools/memory-model/litmus-tests/README +++ b/tools/memory-model/litmus-tests/README @@ -32,6 +32,11 @@ IRIW+poonceonces+OnceOnce.litmus order of a pair of writes, where each write is to a different variable by a different process? +ISA2+pooncelock+pooncelock+pombonce.litmus + Tests whether the ordering provided by a lock-protected S litmus + test is visible to an external process whose accesses are + separated by smp_mb(). + ISA2+poonceonces.litmus As below, but with store-release replaced with WRITE_ONCE() and load-acquire replaced with READ_ONCE().