From: "Paul E. McKenney" <paulmck@kernel.org>
To: Hernan Ponce de Leon <hernan.poncedeleon@huaweicloud.com>
Cc: Jonas Oberhauser <jonas.oberhauser@huaweicloud.com>,
stern@rowland.harvard.edu, parri.andrea@gmail.com,
will@kernel.org, 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, dlustig@nvidia.com,
joel@joelfernandes.org, urezki@gmail.com,
quic_neeraju@quicinc.com, frederic@kernel.org,
linux-kernel@vger.kernel.org, lkmm@lists.linux.dev
Subject: Re: [RFC] tools/memory-model: Rule out OOTA
Date: Tue, 29 Jul 2025 13:34:24 -0700 [thread overview]
Message-ID: <c47d74ef-5eb9-4994-8b73-fbb6eb6bfa8e@paulmck-laptop> (raw)
In-Reply-To: <6f095882-6510-4746-9e59-c24335028237@huaweicloud.com>
On Fri, Jul 25, 2025 at 07:23:23AM +0200, Hernan Ponce de Leon wrote:
> On 7/24/2025 4:14 PM, Paul E. McKenney wrote:
> > On Wed, Jul 23, 2025 at 09:39:05AM -0700, Paul E. McKenney wrote:
> > > On Wed, Jul 23, 2025 at 09:26:32AM +0200, Hernan Ponce de Leon wrote:
> > > > On 7/23/2025 2:43 AM, Paul E. McKenney wrote:
> > > > > On Mon, Jan 06, 2025 at 10:40:03PM +0100, Jonas Oberhauser wrote:
> > > > > > The current LKMM allows out-of-thin-air (OOTA), as evidenced in the following
> > > > > > example shared on this list a few years ago:
> > > > >
> > > > > Apologies for being slow, but I have finally added the litmus tests in
> > > > > this email thread to the https://github.com/paulmckrcu/litmus repo.
> > > >
> > > > I do not understand some of the comments in the preamble of the tests:
> > > >
> > > > (*
> > > > * Result: Never
> > > > *
> > > > * But Sometimes in LKMM as of early 2025, given that 42 is a possible
> > > > * value for things like S19..
> > > > *
> > > > * https://lore.kernel.org/all/20250106214003.504664-1-jonas.oberhauser@huaweicloud.com/
> > > > *)
> > > >
> > > > I see that herd7 reports one of the states to be [b]=S16. Is this supposed
> > > > to be some kind of symbolic state (i.e., any value is possible)?
> > >
> > > Exactly!
> > >
> > > > The value in the "Result" is what we would like the model to say if we would
> > > > have a perfect version of dependencies, right?
> > >
> > > In this case, yes.
> >
> > I should hasten to add that, compiler optimizations being what they are,
> > "perfect" may or may not be attainable, and even if attainable, might
> > not be maintainable.
>
> Yes, I just wanted to clarify if this is what herd7 + the current model are
> saying or what developers should expect.
Good point, and I added explicit words to this effect in the comments
of those aspirational OOTA litmus tests, so thank you!
Thanx, Paul
> Hernan
>
> >
> > I am pretty sure that you all already understood that, but I felt the
> > need to make it explicit. ;-)
> >
> > Thanx, Paul
>
next prev parent reply other threads:[~2025-07-29 20:34 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-01-06 21:40 [RFC] tools/memory-model: Rule out OOTA Jonas Oberhauser
2025-01-07 10:06 ` Peter Zijlstra
2025-01-07 11:02 ` Jonas Oberhauser
2025-01-07 15:46 ` Jonas Oberhauser
2025-01-07 16:09 ` Alan Stern
2025-01-07 18:47 ` Paul E. McKenney
2025-01-08 17:39 ` Jonas Oberhauser
2025-01-08 18:09 ` Paul E. McKenney
2025-01-08 19:17 ` Jonas Oberhauser
2025-01-09 17:54 ` Paul E. McKenney
2025-01-09 18:35 ` Jonas Oberhauser
2025-01-10 14:54 ` Paul E. McKenney
2025-01-10 16:21 ` Jonas Oberhauser
2025-01-13 22:04 ` Paul E. McKenney
2025-01-16 18:40 ` Paul E. McKenney
2025-01-16 19:13 ` Jonas Oberhauser
2025-01-16 19:31 ` Paul E. McKenney
2025-01-16 20:21 ` Jonas Oberhauser
2025-01-16 19:28 ` Jonas Oberhauser
2025-01-16 19:39 ` Paul E. McKenney
2025-01-17 12:08 ` Jonas Oberhauser
2025-01-16 19:08 ` Jonas Oberhauser
2025-01-16 23:02 ` Alan Stern
2025-01-17 8:34 ` Hernan Ponce de Leon
2025-01-17 11:29 ` Jonas Oberhauser
2025-01-17 20:01 ` Alan Stern
2025-01-21 10:36 ` Jonas Oberhauser
2025-01-21 16:39 ` Alan Stern
2025-01-22 3:46 ` Jonas Oberhauser
2025-01-22 19:11 ` Alan Stern
2025-01-17 15:52 ` Alan Stern
2025-01-17 16:45 ` Jonas Oberhauser
2025-01-17 19:02 ` Alan Stern
2025-01-09 20:37 ` Peter Zijlstra
2025-01-09 21:13 ` Paul E. McKenney
2025-01-08 17:33 ` Jonas Oberhauser
2025-01-08 18:47 ` Alan Stern
2025-01-08 19:22 ` Jonas Oberhauser
2025-01-09 16:17 ` Alan Stern
2025-01-09 16:44 ` Jonas Oberhauser
2025-01-09 19:27 ` Alan Stern
2025-01-09 20:09 ` Jonas Oberhauser
2025-01-10 3:12 ` Alan Stern
2025-01-10 12:21 ` Jonas Oberhauser
2025-01-10 21:51 ` Alan Stern
2025-01-11 12:46 ` Jonas Oberhauser
2025-01-11 21:19 ` Alan Stern
2025-01-12 15:55 ` Jonas Oberhauser
2025-01-13 19:43 ` Alan Stern
2025-07-23 0:43 ` Paul E. McKenney
2025-07-23 7:26 ` Hernan Ponce de Leon
2025-07-23 16:39 ` Paul E. McKenney
2025-07-24 14:14 ` Paul E. McKenney
2025-07-25 5:23 ` Hernan Ponce de Leon
2025-07-29 20:34 ` Paul E. McKenney [this message]
2025-07-23 17:13 ` Alan Stern
2025-07-23 17:27 ` Paul E. McKenney
2025-07-23 19:25 ` Alan Stern
2025-07-23 19:57 ` Paul E. McKenney
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