From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1164276AbeBOVvT (ORCPT ); Thu, 15 Feb 2018 16:51:19 -0500 Received: from mail-pg0-f67.google.com ([74.125.83.67]:40901 "EHLO mail-pg0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161926AbeBOVvR (ORCPT ); Thu, 15 Feb 2018 16:51:17 -0500 X-Google-Smtp-Source: AH8x226BKepW5kHo8OeC/WkQc9/o0P0wFMbr4rDh8LRl/mNdEbMYa3AR6cSwTNylAMM50Bedyg3omg== Subject: Re: Trial of conflict resolution of Alan's patch To: "Paul E. McKenney" , Alan Stern Cc: linux-kernel@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, Patrick Bellasi , Akira Yokosawa References: <20180215192914.GA3617@linux.vnet.ibm.com> From: Akira Yokosawa Message-ID: Date: Fri, 16 Feb 2018 06:51:11 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <20180215192914.GA3617@linux.vnet.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018/02/15 11:29:14 -0800, Paul E. McKenney wrote: > On Thu, Feb 15, 2018 at 12:51:56PM -0500, Alan Stern wrote: >> On Fri, 16 Feb 2018, Akira Yokosawa wrote: >> >>> So, I attempted to rebase the patch to current (somewhat old) master of >>> https://github.com/aparri/memory-model. Why? Because the lkmm branch >>> in Paul's -rcu tree doesn't have linux-kernel-hardware.cat. >>> >>> However, after this change, Z6.0+pooncelock+pooncelock+pombonce still >>> has the result "Sometimes". I must have done something wrong in the >>> conflict resolution. >>> >>> Note: I have almost no idea what this patch is doing. I'm just hoping >>> to give a starting point of a discussion. >> >> Yes, that litmus test gives "Sometimes" both with and without the >> patch. But consider instead this slightly changed version of that >> test, in which P2 reads Z instead of writing it: >> >> C Z6.0-variant >> >> {} >> >> P0(int *x, int *y, spinlock_t *mylock) >> { >> spin_lock(mylock); >> WRITE_ONCE(*x, 1); >> WRITE_ONCE(*y, 1); >> spin_unlock(mylock); >> } >> >> P1(int *y, int *z, spinlock_t *mylock) >> { >> int r0; >> >> spin_lock(mylock); >> r0 = READ_ONCE(*y); >> WRITE_ONCE(*z, 1); >> spin_unlock(mylock); >> } >> >> P2(int *x, int *z) >> { >> int r1; >> int r2; >> >> r2 = READ_ONCE(*z); >> smp_mb(); >> r1 = READ_ONCE(*x); >> } >> >> exists (1:r0=1 /\ 2:r2=1 /\ 2:r1=0) >> >> Without the patch, this test gives "Sometimes"; with the patch it gives >> "Never". That is what I thought Paul was talking about originally. >> >> Sorry if my misunderstanding caused too much confusion for other >> people. > > Ah, I did indeed get confused. I have changed the "Result:" for > Z6.0+pooncelock+pooncelock+pombonce.litmus back to "Never", as in > the patch below (which I merged into the patch adding all the > comments). > > I have added the above test as ISA2+pooncelock+pooncelock+pombonce.litmus, > with the Result: of Sometimes with you (Alan) as author and with your > Signed-off-by -- please let me know if you would prefer some other > approach. > > Please change the Result: when sending the proposed patch. Or please let > me know if you would like me to apply the forward-port that Akira sent, > in which case I will add the Result: change to that patch. Or for that > matter, Akira might repost his forward-port of your patch with this change. > Hi, My forward-port patch doesn't apply to the "lkmm" branch. It looks like "linux-kernel-hardware.cat" is intentionally omitted there. Am I guessing right? If this is the case, I can prepare a patch to be applied to "lkmm". But I can't compose a proper change log. So I'd like Alan to post a patch with my SOB appended. Does this approach sound reasonable? Thanks, Akira > Thanx, Paul > > ------------------------------------------------------------------------ > > commit b2950420e1154131c0667f1ac58666bad3a06a69 > Author: Paul E. McKenney > Date: Thu Feb 15 10:35:25 2018 -0800 > > fixup! EXP litmus_tests: Add comments explaining tests' purposes > > Signed-off-by: Paul E. McKenney > > diff --git a/tools/memory-model/litmus-tests/Z6.0+pooncelock+pooncelock+pombonce.litmus b/tools/memory-model/litmus-tests/Z6.0+pooncelock+pooncelock+pombonce.litmus > index fad47258a3e3..95890669859b 100644 > --- a/tools/memory-model/litmus-tests/Z6.0+pooncelock+pooncelock+pombonce.litmus > +++ b/tools/memory-model/litmus-tests/Z6.0+pooncelock+pooncelock+pombonce.litmus > @@ -1,7 +1,7 @@ > C Z6.0+pooncelock+pooncelock+pombonce > > (* > - * Result: Never > + * Result: Somtimes > * > * This example demonstrates that a pair of accesses made by different > * processes each while holding a given lock will not necessarily be >