linux-kernel - Re: [PATCH] random: do not take pool spinlock at boot

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Date:   Sun, 20 Feb 2022 21:34:56 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     linux@...inikbrodowski.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] random: do not take pool spinlock at boot

On Sat, Feb 12, 2022 at 01:28:59AM +0100, Jason A. Donenfeld wrote:
> Since rand_initialize() is run while interrupts are still off and
> nothing else is running, we don't need to repeatedly take and release
> the pool spinlock, especially in the RDSEED loop.
> 
> Cc: Dominik Brodowski <linux@...inikbrodowski.net>
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> ---
> Dominik - I'm still a bit unclear about early boot semantics that you
> seem to know well. Is this patch correct?
> 
>  drivers/char/random.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index d4b692c9de68..8088348190e6 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -966,10 +966,10 @@ int __init rand_initialize(void)
>  			rv = random_get_entropy();
>  			arch_init = false;
>  		}
> -		mix_pool_bytes(&rv, sizeof(rv));
> +		_mix_pool_bytes(&rv, sizeof(rv));
>  	}
> -	mix_pool_bytes(&now, sizeof(now));
> -	mix_pool_bytes(utsname(), sizeof(*(utsname())));
> +	_mix_pool_bytes(&now, sizeof(now));
> +	_mix_pool_bytes(utsname(), sizeof(*(utsname())));
>  
>  	extract_entropy(base_crng.key, sizeof(base_crng.key));
>  	++base_crng.generation;
> -- 
> 2.35.0

Reviewed-by: Eric Biggers <ebiggers@...gle.com>

- Eric