From: Peter Zijlstra <peterz@infradead.org>
To: stern@rowland.harvard.edu, alexander.shishkin@linux.intel.com,
hpa@zytor.com, andrea.parri@amarulasolutions.com,
mingo@kernel.org, paulmck@kernel.org, vincent.weaver@maine.edu,
tglx@linutronix.de, jolsa@redhat.com, acme@redhat.com,
torvalds@linux-foundation.org, linux-kernel@vger.kernel.org,
eranian@google.com, will@kernel.org
Cc: linux-tip-commits@vger.kernel.org
Subject: Re: [tip:locking/core] tools/memory-model: Add extra ordering for locks and remove it for ordinary release/acquire
Date: Wed, 8 Sep 2021 13:00:26 +0200 [thread overview]
Message-ID: <YTiXyiA92dM9726M@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <tip-6e89e831a90172bc3d34ecbba52af5b9c4a447d1@git.kernel.org>
On Tue, Oct 02, 2018 at 03:11:10AM -0700, tip-bot for Alan Stern wrote:
> Commit-ID: 6e89e831a90172bc3d34ecbba52af5b9c4a447d1
> Gitweb: https://git.kernel.org/tip/6e89e831a90172bc3d34ecbba52af5b9c4a447d1
> Author: Alan Stern <stern@rowland.harvard.edu>
> AuthorDate: Wed, 26 Sep 2018 11:29:17 -0700
> Committer: Ingo Molnar <mingo@kernel.org>
> CommitDate: Tue, 2 Oct 2018 10:28:01 +0200
>
> tools/memory-model: Add extra ordering for locks and remove it for ordinary release/acquire
>
> More than one kernel developer has expressed the opinion that the LKMM
> should enforce ordering of writes by locking. In other words, given
> the following code:
>
> WRITE_ONCE(x, 1);
> spin_unlock(&s):
> spin_lock(&s);
> WRITE_ONCE(y, 1);
>
> the stores to x and y should be propagated in order to all other CPUs,
> even though those other CPUs might not access the lock s. In terms of
> the memory model, this means expanding the cumul-fence relation.
Let me revive this old thread... recently we ran into the case:
WRITE_ONCE(x, 1);
spin_unlock(&s):
spin_lock(&r);
WRITE_ONCE(y, 1);
which is distinct from the original in that UNLOCK and LOCK are not on
the same variable.
I'm arguing this should still be RCtso by reason of:
spin_lock() requires an atomic-acquire which:
TSO-arch) implies smp_mb()
ARM64) is RCsc for any stlr/ldar
Power) LWSYNC
Risc-V) fence r , rw
*) explicitly has smp_mb()
However, Boqun points out that the memory model disagrees, per:
https://lkml.kernel.org/r/YTI2UjKy+C7LeIf+@boqun-archlinux
Is this an error/oversight of the memory model, or did I miss a subtlety
somewhere?
next prev parent reply other threads:[~2021-09-08 11:01 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-26 18:28 [PATCH memory-model 0/5] Updates to the formal memory model Paul E. McKenney
2018-09-26 18:29 ` [PATCH memory-model 1/5] tools/memory-model: Add litmus-test naming scheme Paul E. McKenney
2018-10-02 10:10 ` [tip:locking/core] " tip-bot for Paul E. McKenney
2018-09-26 18:29 ` [PATCH memory-model 2/5] tools/memory-model: Add extra ordering for locks and remove it for ordinary release/acquire Paul E. McKenney
2018-10-02 10:11 ` [tip:locking/core] " tip-bot for Alan Stern
2021-09-08 11:00 ` Peter Zijlstra [this message]
2021-09-08 11:44 ` Peter Zijlstra
2021-09-08 14:42 ` Alan Stern
2021-09-08 15:12 ` Peter Zijlstra
2021-09-08 16:08 ` Linus Torvalds
2021-09-09 7:25 ` Peter Zijlstra
2021-09-09 13:35 ` Will Deacon
2021-09-09 17:02 ` Linus Torvalds
2021-09-09 18:59 ` Alan Stern
2021-09-09 17:03 ` Dan Lustig
2021-09-09 18:00 ` Paul E. McKenney
2021-09-10 14:20 ` Boqun Feng
2021-09-10 15:33 ` Palmer Dabbelt
2021-09-10 16:36 ` Alan Stern
2021-09-10 17:12 ` Peter Zijlstra
2021-09-10 17:56 ` Alan Stern
2021-09-10 17:17 ` Peter Zijlstra
2021-09-12 0:26 ` Boqun Feng
2021-09-10 0:01 ` Boqun Feng
2021-09-10 5:37 ` Boqun Feng
2021-09-10 9:33 ` Peter Zijlstra
2021-09-10 10:04 ` Boqun Feng
2021-09-10 13:48 ` Dan Lustig
2021-09-10 14:15 ` Boqun Feng
2021-09-09 17:46 ` Paul E. McKenney
2021-09-10 11:08 ` Will Deacon
2021-09-17 3:21 ` Nicholas Piggin
2021-09-17 5:31 ` Nicholas Piggin
2021-09-17 14:36 ` Michael Ellerman
2018-09-26 18:29 ` [PATCH memory-model 3/5] tools/memory-model: Fix a README typo Paul E. McKenney
2018-10-02 10:11 ` [tip:locking/core] " tip-bot for SeongJae Park
2018-09-26 18:29 ` [PATCH memory-model 4/5] tools/memory-model: Add more LKMM limitations Paul E. McKenney
2018-10-02 10:12 ` [tip:locking/core] " tip-bot for Paul E. McKenney
2018-09-26 18:29 ` [PATCH memory-model 5/5] doc: Replace smp_cond_acquire() with smp_cond_load_acquire() Paul E. McKenney
2018-10-02 10:12 ` [tip:locking/core] locking/memory-barriers: " tip-bot for Andrea Parri
2018-10-02 8:28 ` [PATCH memory-model 0/5] Updates to the formal memory model Ingo Molnar
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YTiXyiA92dM9726M@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=acme@redhat.com \
--cc=alexander.shishkin@linux.intel.com \
--cc=andrea.parri@amarulasolutions.com \
--cc=eranian@google.com \
--cc=hpa@zytor.com \
--cc=jolsa@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-tip-commits@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=paulmck@kernel.org \
--cc=stern@rowland.harvard.edu \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.org \
--cc=vincent.weaver@maine.edu \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).