linux-kernel - Re: [PATCH] locking/atomic: cmpxchg: Make __generic_cmpxchg_local compare against zero-extended 'old' value

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Message-Id: <7b4e8b07-4691-4af3-ae8b-ba612b6af595@app.fastmail.com>
Date:   Wed, 01 Mar 2023 17:22:11 +0100
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Matt Evans" <mev@...osinc.com>
Cc:     linux-kernel@...r.kernel.org,
        Linux-Arch <linux-arch@...r.kernel.org>,
        "Palmer Dabbelt" <palmer@...osinc.com>
Subject: Re: [PATCH] locking/atomic: cmpxchg: Make __generic_cmpxchg_local compare
 against zero-extended 'old' value

On Wed, Mar 1, 2023, at 16:19, Matt Evans wrote:
>> On 26 Feb 2023, at 10:13, Arnd Bergmann <arnd@...db.de> wrote:
>
> Proposed patch LGTM, but one query:  are the casts in 
> arch_[cmp]xchg()’s args necessary?  The new masks should deal with the 
> issue (and consistency would imply same for all other users of 
> arch_cmpxchg(), not ideal).

I don't think they are necessary, but I'd like to stay on the
safe side here since there are so many different implementations of
arch_cmpxchg() across architectures that it's likely that I missed
one that has a similar but, or that another one will get added
in the future.

> FWIW (including the casts in atomic.h, if you prefer):
>
> Reviewed-by: Matt Evans <mev@...osinc.com>

Thanks!

     Arnd