linux-kernel - Re: [PATCH 2/2] random: move initialization out of reseeding hot path

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Message-ID: <Yn35k+yyrvgAt3tb@owl.dominikbrodowski.net>
Date:   Fri, 13 May 2022 08:24:19 +0200
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] random: move initialization out of reseeding hot path

Am Mon, May 09, 2022 at 02:14:09PM +0200 schrieb Jason A. Donenfeld:
> Initialization happens once -- by way of credit_init_bits() -- and then
> it never happens again. Therefore, it doesn't need to be in
> crng_reseed(), which is a hot path that is called multiple times. It
> also doesn't make sense to have there, as initialization activity is
> better associated with initialization routines.
> 
> After the prior commit, crng_reseed() now won't be called by multiple
> concurrent callers, which means that we can safely move the
> "finialize_init" logic into crng_init_bits() unconditionally.
> 
> Cc: Dominik Brodowski <linux@...inikbrodowski.net>
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> ---
>  drivers/char/random.c | 43 +++++++++++++++++++------------------------
>  1 file changed, 19 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index 79409cf27a25..1598bb40376e 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -266,7 +266,6 @@ static void crng_reseed(void)
>  	unsigned long flags;
>  	unsigned long next_gen;
>  	u8 key[CHACHA_KEY_SIZE];
> -	bool finalize_init = false;
>  
>  	extract_entropy(key, sizeof(key));
>  
> @@ -283,28 +282,9 @@ static void crng_reseed(void)
>  		++next_gen;
>  	WRITE_ONCE(base_crng.generation, next_gen);
>  	WRITE_ONCE(base_crng.birth, jiffies);
> -	if (!crng_ready()) {
> -		crng_init = CRNG_READY;
> -		finalize_init = true;
> -	}
> +	crng_init = CRNG_READY;

Why unconditionally (you revert that bit in the static branch patch and make
it conditional again; so I see no reason for that here)?

Otherwise, looks good:

	Reviewed-by: Dominik Brodowski <linux@...inikbrodowski.net>

Thanks,
	Dominik