linux-kernel - Re: [PATCH] rtmutex: Add acquire semantics for rtmutex lock acquisition

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Message-ID: <Y5yavm77lWLH+IWj@linutronix.de>
Date:   Fri, 16 Dec 2022 17:20:14 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Will Deacon <will@...nel.org>
Cc:     Mel Gorman <mgorman@...hsingularity.net>,
        Peter Zijlstra <peterz@...radead.org>, Jan Kara <jack@...e.cz>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Pierre Gondois <pierre.gondois@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Davidlohr Bueso <dave@...olabs.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-RT <linux-rt-users@...r.kernel.org>
Subject: Re: [PATCH] rtmutex: Add acquire semantics for rtmutex lock
 acquisition

On 2022-12-16 15:58:04 [+0000], Will Deacon wrote:
> I guess bigeasy can give the weaker barrier a try if he has the time, but
> otherwise we can leave the change as-is.

I can't give a try because I have no HW. All I contributed here so far
was based on what you wrote in the previous email and then I spotted the
lack of the barrier of any sorts and asked about it.
I _would_ assume that the cmpxchg_barrier() here would work but I'm far
from knowing.
If the explicit barrier after the cmpxchg_relaxed() is what you two
agree on and it is better/ cheaper/ more obvious then fine. Do it ;)

> Cheers,
> 
> Will

Sebastian