From: Peter Zijlstra <peterz@infradead.org>
To: Florian Weimer <fweimer@redhat.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>,
Daniel Xu <dxu@dxuuu.xyz>,
mingo@redhat.com, will@kernel.org, longman@redhat.com,
boqun.feng@gmail.com, linux-kernel@vger.kernel.org,
linux-toolchains@vger.kernel.org
Subject: Re: [PATCH] seqlock: Use WRITE_ONCE() when updating sequence
Date: Thu, 19 Dec 2024 18:53:33 +0100 [thread overview]
Message-ID: <20241219175333.GE26279@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <87v7vfwrj8.fsf@oldenburg.str.redhat.com>
On Thu, Dec 19, 2024 at 05:45:15PM +0100, Florian Weimer wrote:
> > Peter's "(*(volatile unsigned int *)&s->sequence)++;" qualifies as sane.
>
> I think the reference was originally to machine code.
Correct; however more tinkering with godbolt got me:
https://godbolt.org/z/6xoxjdYPx
Where we can see that clang can even optimize the WRITE_ONCE(foo,
READ_ONCE(foo) + 1) case, which I though it would not be able to do.
So perhaps we just need to get GCC fixed.
next prev parent reply other threads:[~2024-12-19 17:53 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-12-17 23:17 [PATCH] seqlock: Use WRITE_ONCE() when updating sequence Daniel Xu
2024-12-18 3:30 ` Waiman Long
2024-12-18 15:45 ` Paul E. McKenney
2024-12-18 16:10 ` Waiman Long
2024-12-18 16:57 ` Paul E. McKenney
2024-12-18 18:38 ` Waiman Long
2024-12-18 18:52 ` Paul E. McKenney
2024-12-18 20:09 ` Waiman Long
2024-12-18 10:30 ` Peter Zijlstra
2024-12-18 15:43 ` Paul E. McKenney
2024-12-18 16:23 ` Peter Zijlstra
2024-12-18 16:29 ` Peter Zijlstra
2024-12-18 16:59 ` Paul E. McKenney
2024-12-18 17:12 ` Peter Zijlstra
2024-12-18 19:15 ` Paul E. McKenney
2024-12-18 19:56 ` Florian Weimer
2024-12-19 16:10 ` Paul E. McKenney
2024-12-19 16:45 ` Florian Weimer
2024-12-19 17:48 ` Paul E. McKenney
2024-12-19 17:53 ` Peter Zijlstra [this message]
2024-12-19 16:34 ` Will Deacon
2024-12-19 17:53 ` Paul E. McKenney
2024-12-19 17:58 ` Will Deacon
2024-12-19 18:06 ` Paul E. McKenney
2024-12-19 18:31 ` Will Deacon
2024-12-20 17:40 ` Paul E. McKenney
2025-01-25 0:31 ` Daniel Xu
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