From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755099AbeBUSAD (ORCPT ); Wed, 21 Feb 2018 13:00:03 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:45978 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754135AbeBUSAB (ORCPT ); Wed, 21 Feb 2018 13:00:01 -0500 Date: Wed, 21 Feb 2018 10:00:16 -0800 From: "Paul E. McKenney" To: Alan Stern Cc: Andrea Parri , Akira Yokosawa , Kernel development list , mingo@kernel.org, Will Deacon , peterz@infradead.org, boqun.feng@gmail.com, npiggin@gmail.com, dhowells@redhat.com, Jade Alglave , Luc Maranget , Patrick Bellasi Subject: Re: [PATCH] tools/memory-model: update: remove rb-dep, smp_read_barrier_depends, and lockless_dereference Reply-To: paulmck@linux.vnet.ibm.com References: <20180221160602.GD3617@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: 18022117-0036-0000-0000-000002C41160 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008571; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000254; SDB=6.00993056; UDB=6.00504564; IPR=6.00772401; MB=3.00019675; MTD=3.00000008; XFM=3.00000015; UTC=2018-02-21 17:59:57 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18022117-0037-0000-0000-0000436A53C9 Message-Id: <20180221180016.GK3617@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-1802210218 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 21, 2018 at 12:15:56PM -0500, Alan Stern wrote: > Commit bf28ae562744 ("tools/memory-model: Remove rb-dep, > smp_read_barrier_depends, and lockless_dereference") was accidentally > merged too early, while it was still in RFC form. This patch adds in > the missing pieces. > > Akira pointed out some typos in the original patch, and he noted that > cheatsheet.txt should be updated to indicate how unsuccessful RMW > operations relate to address dependencies. > > Andrea pointed out that the macro for rcu_dereference() in linux.def > should now use the "once" annotation instead of "deref". He also > suggested that the comments should mention commit 5a8897cc7631 > ("locking/atomics/alpha: Add smp_read_barrier_depends() to > _release()/_relaxed() atomics") as an important precursor, and he > contributed commit cb13b424e986 ("locking/xchg/alpha: Add > unconditional memory barrier to cmpxchg()"), another prerequisite. > > Signed-off-by: Alan Stern > Suggested-by: Akira Yokosawa > Suggested-by: Andrea Parri > Fixes: bf28ae562744 ("tools/memory-model: Remove rb-dep, smp_read_barrier_depends, and lockless_dereference") Queued, thank you! Thanx, Paul > --- > > tools/memory-model/Documentation/cheatsheet.txt | 6 +++--- > tools/memory-model/Documentation/explanation.txt | 4 ++-- > tools/memory-model/linux-kernel.def | 2 +- > 3 files changed, 6 insertions(+), 6 deletions(-) > > Index: usb-4.x/tools/memory-model/Documentation/cheatsheet.txt > =================================================================== > --- usb-4.x.orig/tools/memory-model/Documentation/cheatsheet.txt > +++ usb-4.x/tools/memory-model/Documentation/cheatsheet.txt > @@ -1,11 +1,11 @@ > Prior Operation Subsequent Operation > --------------- --------------------------- > C Self R W RWM Self R W DR DW RMW SV > - __ ---- - - --- ---- - - -- -- --- -- > + -- ---- - - --- ---- - - -- -- --- -- > > Store, e.g., WRITE_ONCE() Y Y > -Load, e.g., READ_ONCE() Y Y Y > -Unsuccessful RMW operation Y Y Y > +Load, e.g., READ_ONCE() Y Y Y Y > +Unsuccessful RMW operation Y Y Y Y > rcu_dereference() Y Y Y Y > Successful *_acquire() R Y Y Y Y Y Y > Successful *_release() C Y Y Y W Y > Index: usb-4.x/tools/memory-model/Documentation/explanation.txt > =================================================================== > --- usb-4.x.orig/tools/memory-model/Documentation/explanation.txt > +++ usb-4.x/tools/memory-model/Documentation/explanation.txt > @@ -826,7 +826,7 @@ A-cumulative; they only affect the propa > executed on C before the fence (i.e., those which precede the fence in > program order). > > -read_lock(), rcu_read_unlock(), and synchronize_rcu() fences have > +read_read_lock(), rcu_read_unlock(), and synchronize_rcu() fences have > other properties which we discuss later. > > > @@ -1138,7 +1138,7 @@ final effect is that even though the two > program order, it appears that they aren't. > > This could not have happened if the local cache had processed the > -incoming stores in FIFO order. In constrast, other architectures > +incoming stores in FIFO order. By contrast, other architectures > maintain at least the appearance of FIFO order. > > In practice, this difficulty is solved by inserting a special fence > Index: usb-4.x/tools/memory-model/linux-kernel.def > =================================================================== > --- usb-4.x.orig/tools/memory-model/linux-kernel.def > +++ usb-4.x/tools/memory-model/linux-kernel.def > @@ -13,7 +13,7 @@ WRITE_ONCE(X,V) { __store{once}(X,V); } > smp_store_release(X,V) { __store{release}(*X,V); } > smp_load_acquire(X) __load{acquire}(*X) > rcu_assign_pointer(X,V) { __store{release}(X,V); } > -rcu_dereference(X) __load{deref}(X) > +rcu_dereference(X) __load{once}(X) > > // Fences > smp_mb() { __fence{mb} ; } >