linux-kernel - Re: [PATCH 1/2 v2] lib/vsprintf: Remove static_branch_likely() from __ptr_to

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Date:   Mon, 1 Aug 2022 14:11:33 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        John Ogness <john.ogness@...utronix.de>,
        Mike Galbraith <efault@....de>, Petr Mladek <pmladek@...e.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Theodore Ts'o <tytso@....edu>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/2 v2] lib/vsprintf: Remove static_branch_likely() from
 __ptr_to_hashval().

On Fri, Jul 29, 2022 at 05:47:15PM +0200, Sebastian Andrzej Siewior wrote:
> Using static_branch_likely() to signal that ptr_key has been filled is a
> bit much given that it is not a fast path.
> 
> Replace static_branch_likely() with bool for condition and a memory
> barrier for ptr_key.
> 
> Suggested-by: Petr Mladek <pmladek@...e.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  lib/vsprintf.c |   19 ++++++++-----------
>  1 file changed, 8 insertions(+), 11 deletions(-)
> 
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -750,12 +750,7 @@ static int __init debug_boot_weak_hash_e
>  }
>  early_param("debug_boot_weak_hash", debug_boot_weak_hash_enable);
>  
> -static DEFINE_STATIC_KEY_FALSE(filled_random_ptr_key);
> -
> -static void enable_ptr_key_workfn(struct work_struct *work)
> -{
> -	static_branch_enable(&filled_random_ptr_key);
> -}
> +static bool filled_random_ptr_key;

This should be __read_mostly, right? Just like ptr_key.

Jason