linux-kernel - Re: [PATCH] Documentation/atomic_t: Document cmpxchg() vs try

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Message-ID: <20210705152136.GA19127@willie-the-truck>
Date:   Mon, 5 Jul 2021 16:21:36 +0100
From:   Will Deacon <will@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Xu, Yanfei" <yanfei.xu@...driver.com>, mingo@...hat.com,
        longman@...hat.com, boqun.feng@...il.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Documentation/atomic_t: Document cmpxchg() vs
 try_cmpxchg()

On Mon, Jul 05, 2021 at 05:07:41PM +0200, Peter Zijlstra wrote:
> On Mon, Jul 05, 2021 at 04:00:01PM +0200, Peter Zijlstra wrote:
> 
> > No, when try_cmpxchg() fails it will update oldp. This is the reason old
> > is now a pointer too.
> 
> Since you're not the first person confused by this, does the below
> clarify?
> 
> ---
> Subject: Documentation/atomic_t: Document cmpxchg() vs try_cmpxchg()
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Mon Jul  5 17:00:24 CEST 2021
> 
> There seems to be a significant amount of confusion around the 'new'
> try_cmpxchg(), despite this being more like the C11
> atomic_compare_exchange_*() family. Add a few words of clarification
> on how cmpxchg() and try_cmpxchg() relate to one another.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  Documentation/atomic_t.txt |   41 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 41 insertions(+)

With the "CMPXHG" typo fixed:

Acked-by: Will Deacon <will@...nel.org>

Will