From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Alan Stern <stern@rowland.harvard.edu>,
Andrea Parri <parri.andrea@gmail.com>,
Akira Yokosawa <akiyks@gmail.com>,
Kernel development list <linux-kernel@vger.kernel.org>,
mingo@kernel.org, Will Deacon <will.deacon@arm.com>,
boqun.feng@gmail.com, npiggin@gmail.com, dhowells@redhat.com,
Jade Alglave <j.alglave@ucl.ac.uk>,
Luc Maranget <luc.maranget@inria.fr>,
Patrick Bellasi <patrick.bellasi@arm.com>
Subject: Re: [PATCH] tools/memory-model: remove rb-dep, smp_read_barrier_depends, and lockless_dereference
Date: Tue, 20 Feb 2018 06:49:39 -0800 [thread overview]
Message-ID: <20180220144939.GG3617@linux.vnet.ibm.com> (raw)
In-Reply-To: <20180219202844.GW25201@hirez.programming.kicks-ass.net>
On Mon, Feb 19, 2018 at 09:28:44PM +0100, Peter Zijlstra wrote:
> On Mon, Feb 19, 2018 at 11:41:23AM -0800, Paul E. McKenney wrote:
> > On Mon, Feb 19, 2018 at 12:14:45PM -0500, Alan Stern wrote:
> > > This leaves us with a question: Do we want to change the kernel by
> > > adding memory barriers after unsuccessful RMW operations on Alpha, or
> > > do we want to change the model by excluding such operations from
> > > address dependencies?
> >
> > I vote for adding the barrier on Alpha. However, I don't know of any
> > code in the Linux kernel that relies on read-to-read address dependency
> > ordering headed by a failing RMW operation, so I don't feel all that
> > strongly about this.
>
> Right, but not knowing doesn't mean doesn't exist, and most certainly
> doesn't mean will never exist.
Fair enough, safety first!
> > > Note that operations like atomic_add_unless() already include memory
> > > barriers.
> >
> > And I don't see an atomic_add_unless_relaxed(), so we are good on this
> > one. So far, anyway! ;-)
>
> Not the point, add_unless() is a conditional operation, and therefore
> doesn't need to imply anything when failing.
Plus it doesn't return a pointer, so there is no problem with dereferences.
Unless someone wants to use its return value as an array index and rely
on dependency ordering to the array, but I would NAK that use case.
Thanx, Paul
next prev parent reply other threads:[~2018-02-20 14:49 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-09 14:18 [PATCH RFC tools/lkmm] Miscellaneous fixes Paul E. McKenney
2018-02-09 14:20 ` [PATCH RFC tip/lkmm 01/10] tools/memory-model: Clarify the origin/scope of the tool name Paul E. McKenney
2018-02-09 14:20 ` [PATCH RFC tip/lkmm 02/10] MAINTAINERS: Add the Memory Consistency Model subsystem Paul E. McKenney
2018-02-09 14:20 ` [PATCH RFC tip/lkmm 03/10] MAINTAINERS: List file memory-barriers.txt within the LKMM entry Paul E. McKenney
2018-02-09 14:20 ` [PATCH RFC tip/lkmm 04/10] EXP litmus_tests: Add comments explaining tests' purposes Paul E. McKenney
2018-02-09 18:46 ` Alan Stern
2018-02-10 1:05 ` Paul E. McKenney
2018-02-09 14:20 ` [PATCH RFC tip/lkmm 05/10] README: Fix a couple of punctuation errors Paul E. McKenney
2018-02-09 14:20 ` [PATCH RFC tip/lkmm 06/10] EXP MAINTAINERS: Add the "LKMM" acronym Paul E. McKenney
2018-02-09 14:20 ` [PATCH RFC tip/lkmm 07/10] MAINTAINERS: Add Akira Yokosawa as an LKMM reviewer Paul E. McKenney
2018-02-09 14:20 ` [PATCH RFC tip/lkmm 08/10] EXP Remove understore from smp_mb__before_atomic() workings Paul E. McKenney
2018-02-15 22:30 ` Andrea Parri
2018-02-15 22:49 ` Paul E. McKenney
2018-02-15 23:19 ` Andrea Parri
2018-02-15 23:32 ` Paul E. McKenney
2018-02-09 14:20 ` [PATCH RFC tip/lkmm 09/10] EXP Remove underscore from smp_mb__after_atomic() workings Paul E. McKenney
2018-02-09 14:20 ` [PATCH RFC tip/lkmm 10/10] EXP Remove underscores from smp_mb__after_spinlock() workings Paul E. McKenney
2018-02-09 16:02 ` [PATCH RFC tools/lkmm] Miscellaneous fixes Akira Yokosawa
2018-02-09 16:06 ` [PATCH] tools/memory-model: Restore compat with herd7 7.47 ("-" -> "_") Akira Yokosawa
2018-02-09 23:46 ` [PATCH v2] tools/memory-model: Make " Akira Yokosawa
2018-02-10 1:07 ` Paul E. McKenney
2018-02-10 3:03 ` Akira Yokosawa
2018-02-11 11:51 ` Ingo Molnar
2018-02-13 1:38 ` Paul E. McKenney
2018-02-13 8:32 ` Ingo Molnar
2018-02-14 22:20 ` Akira Yokosawa
2018-02-14 22:52 ` Paul E. McKenney
2018-02-15 15:10 ` Alan Stern
2018-02-15 15:58 ` Trial of conflict resolution of Alan's patch Akira Yokosawa
2018-02-15 17:51 ` Alan Stern
2018-02-15 19:29 ` Paul E. McKenney
2018-02-15 21:51 ` Akira Yokosawa
2018-02-16 15:18 ` Alan Stern
2018-02-16 15:47 ` Andrea Parri
2018-02-16 16:53 ` Paul E. McKenney
2018-02-16 22:22 ` [PATCH] tools/memory-model: remove rb-dep, smp_read_barrier_depends, and lockless_dereference Alan Stern
2018-02-16 23:22 ` Akira Yokosawa
2018-02-17 0:39 ` Paul E. McKenney
2018-02-21 15:00 ` Alan Stern
2018-02-21 16:06 ` Paul E. McKenney
2018-02-21 16:51 ` Ingo Molnar
2018-02-21 17:53 ` Paul E. McKenney
2018-02-21 17:15 ` [PATCH] tools/memory-model: update: " Alan Stern
2018-02-21 17:58 ` Andrea Parri
2018-02-21 18:14 ` Paul E. McKenney
2018-02-21 18:00 ` Paul E. McKenney
2018-02-21 22:29 ` Akira Yokosawa
2018-02-24 3:22 ` Akira Yokosawa
2018-02-24 3:30 ` Paul E. McKenney
2018-02-24 14:36 ` Andrea Parri
2018-02-24 16:49 ` Alan Stern
2018-02-24 18:08 ` Paul E. McKenney
2018-02-24 22:47 ` Akira Yokosawa
2018-02-25 22:33 ` Paul E. McKenney
2018-02-17 3:25 ` [PATCH] tools/memory-model: " Andrea Parri
2018-02-17 15:14 ` Andrea Parri
2018-02-19 17:14 ` Alan Stern
2018-02-19 17:43 ` Peter Zijlstra
2018-02-19 17:44 ` Peter Zijlstra
2018-02-20 14:48 ` Paul E. McKenney
2018-02-20 15:17 ` Andrea Parri
2018-02-20 16:11 ` Paul E. McKenney
2018-02-19 19:41 ` Paul E. McKenney
2018-02-19 20:28 ` Peter Zijlstra
2018-02-20 14:49 ` Paul E. McKenney [this message]
2018-02-20 15:11 ` Alan Stern
2018-02-20 16:10 ` Paul E. McKenney
2018-02-20 9:33 ` Andrea Parri
2018-02-20 9:51 ` Peter Zijlstra
2018-02-20 15:38 ` Alan Stern
2018-02-15 22:05 ` Trial of conflict resolution of Alan's patch Andrea Parri
2018-02-15 22:41 ` Paul E. McKenney
2018-02-18 15:46 ` [PATCH v2] tools/memory-model: Make compat with herd7 7.47 ("-" -> "_") Akira Yokosawa
2018-02-20 14:57 ` Paul E. McKenney
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