From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S938916AbeBUR7J (ORCPT ); Wed, 21 Feb 2018 12:59:09 -0500 Received: from mail-wr0-f196.google.com ([209.85.128.196]:43692 "EHLO mail-wr0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753941AbeBUR7G (ORCPT ); Wed, 21 Feb 2018 12:59:06 -0500 X-Google-Smtp-Source: AH8x224+XbjDN5OLK4sxWd8OtJSKsG5+74i2BfNENKT4eSk69y6+tr1x2+9fHs4jpp+16qVh5Ss3eA== Date: Wed, 21 Feb 2018 18:58:57 +0100 From: Andrea Parri To: Alan Stern Cc: "Paul E. McKenney" , 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 Message-ID: <20180221175857.GA23000@andrea> 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/1.5.24 (2015-08-30) 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") Acked-by: Andrea Parri Thanks, Andrea > > --- > > 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} ; } >