linux-kernel - Re: [PATCH] random: Use try_cmpxchg in _credit_init

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Message-ID: <YtMDeHO93SQh0ufA@zx2c4.com>
Date:   Sat, 16 Jul 2022 20:29:12 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Uros Bizjak <ubizjak@...il.com>
Cc:     linux-kernel@...r.kernel.org, Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH] random: Use try_cmpxchg in _credit_init_bits

Hi Uros,

On Thu, Jul 14, 2022 at 08:28:22PM +0200, Uros Bizjak wrote:
> Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
> _credit_init_bits. x86 CMPXCHG instruction returns success in ZF flag,
> so this change saves a compare after cmpxchg (and related move
> instruction in front of cmpxchg).
> 
> Also, try_cmpxchg implicitly assigns old *ptr value to "old"
> when cmpxchg fails, enabling further code simplifications.
> 
> No functional change intended.

Applied as:
  https://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git/commit/?id=6a66e096619e3a737297eb2f9f535a287af43a95

Thanks for the patch.

Jason