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Message-ID: <ZKUWPKWAnjZvqsgL@Boquns-Mac-mini.local>
Date: Wed, 5 Jul 2023 00:05:32 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Olivier Dion <odion@...icios.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, rnk@...gle.com,
Alan Stern <stern@...land.harvard.edu>,
Andrea Parri <parri.andrea@...il.com>,
Will Deacon <will@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Nicholas Piggin <npiggin@...il.com>,
David Howells <dhowells@...hat.com>,
Jade Alglave <j.alglave@....ac.uk>,
Luc Maranget <luc.maranget@...ia.fr>,
"Paul E. McKenney" <paulmck@...nel.org>,
Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
linux-arch@...r.kernel.org, gcc@....gnu.org, llvm@...ts.linux.dev
Subject: Re: [RFC] Bridging the gap between the Linux Kernel Memory
Consistency Model (LKMM) and C11/C++11 atomics
On Mon, Jul 03, 2023 at 03:20:31PM -0400, Olivier Dion wrote:
[...]
> NOTE: On x86-64, we found at least one corner case [7] with Clang where
> a RELEASE exchange is optimized to a RELEASE store, when the returned
> value of the exchange is unused, breaking the above expectations.
> Although this type of optimization respect the standard "as-if"
> statement, we question its pertinence since a user should simply do a
> RELEASE store instead of an exchange in that case. With the
> introduction of these new primitives, these type of optimizations should
> be revisited.
>
FWIW, this is actually a LLVM bug:
https://github.com/llvm/llvm-project/issues/60418
Regards,
Boqun
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