linux-kernel - Re: [PATCH 1/3] crypto: skcipher

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Date:   Tue, 20 Dec 2022 11:54:06 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Robert Elliott <elliott@....com>
Cc:     davem@...emloft.net, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] crypto: skcipher - always yield at end of walk

On Mon, Dec 19, 2022 at 02:37:31PM -0600, Robert Elliott wrote:
>
> diff --git a/crypto/skcipher.c b/crypto/skcipher.c
> index 0ecab31cfe79..cdead632117a 100644
> --- a/crypto/skcipher.c
> +++ b/crypto/skcipher.c
> @@ -153,13 +153,20 @@ int skcipher_walk_done(struct skcipher_walk *walk, int err)
>  	scatterwalk_done(&walk->in, 0, nbytes);
>  	scatterwalk_done(&walk->out, 1, nbytes);
>  
> -	if (nbytes) {
> -		crypto_yield(walk->flags & SKCIPHER_WALK_SLEEP ?
> -			     CRYPTO_TFM_REQ_MAY_SLEEP : 0);
> +	/*
> +	 * Allow scheduler to use the CPU since it has been busy,
> +	 * regardless of whether another loop pass is due
> +	 */
> +	crypto_yield(walk->flags & SKCIPHER_WALK_SLEEP ?
> +		     CRYPTO_TFM_REQ_MAY_SLEEP : 0);
> +
> +	if (nbytes)
>  		return skcipher_walk_next(walk);
> -	}
>  
>  finish:
> +	crypto_yield(walk->flags & SKCIPHER_WALK_SLEEP ?
> +		     CRYPTO_TFM_REQ_MAY_SLEEP : 0);
> +

You're calling crypto_yield twice if nbytes == 0.  How about
deleting the second crypto_yield call because the only case
where it would matter is when n == 0.

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt