linux-kernel - Re: [tip: locking/core] locking/pvqspinlock: Use try_cmpxchg_acquire() in trylock_clear

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Message-ID: <CAHk-=wgaxi4Sau27C5yo3vty67DHz-f4L6SSOvmx1K2fQU2B_g@mail.gmail.com>
Date: Thu, 11 Apr 2024 09:31:26 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: linux-kernel@...r.kernel.org
Cc: linux-tip-commits@...r.kernel.org, Uros Bizjak <ubizjak@...il.com>, 
	Ingo Molnar <mingo@...nel.org>, Waiman Long <longman@...hat.com>, x86@...nel.org
Subject: Re: [tip: locking/core] locking/pvqspinlock: Use try_cmpxchg_acquire()
 in trylock_clear_pending()

On Thu, 11 Apr 2024 at 06:33, tip-bot2 for Uros Bizjak
<tip-bot2@...utronix.de> wrote:
>
> Use try_cmpxchg_acquire(*ptr, &old, new) instead of
> cmpxchg_relaxed(*ptr, old, new) == old in trylock_clear_pending().

The above commit message is horribly confusing and wrong.

I was going "that's not right", because it says "use acquire instead
of relaxed" memory ordering, and then goes on to say "No functional
change intended".

But it turns out the *code* was always acquire, and it's only the
commit message that is wrong, presumably due to a bit too much
cut-and-paste.

But please fix the commit message, and use the right memory ordering
in the explanations too.

            Linus