linux-kernel - Re: [PATCH] padata: use alignment when calculating the number of worker threads

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Date:   Wed, 1 Mar 2023 11:36:47 -0500
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     Anthony Yznaga <anthony.yznaga@...cle.com>
Cc:     steffen.klassert@...unet.com, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] padata: use alignment when calculating the number of
 worker threads

On Wed, Feb 22, 2023 at 04:33:12PM -0800, Anthony Yznaga wrote:
> For multithreaded jobs the computed chunk size is rounded up by the
> caller-specified alignment. However, the number of worker threads to
> use is computed using the minimum chunk size without taking alignment
> into account. A sufficiently large alignment value can result in too
> many worker threads being allocated for the job.
> 
> Signed-off-by: Anthony Yznaga <anthony.yznaga@...cle.com>

No effect for now since the page init code uses the same align and
min_chunk, but it protects future users from this problem so

Acked-by: Daniel Jordan <daniel.m.jordan@...cle.com>

Thanks.

> ---
>  kernel/padata.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/padata.c b/kernel/padata.c
> index e007b8a4b738..4abc536ecdb1 100644
> --- a/kernel/padata.c
> +++ b/kernel/padata.c
> @@ -491,7 +491,7 @@ void __init padata_do_multithreaded(struct padata_mt_job *job)
>  		return;
>  
>  	/* Ensure at least one thread when size < min_chunk. */
> -	nworks = max(job->size / job->min_chunk, 1ul);
> +	nworks = max(job->size / max(job->min_chunk, job->align), 1ul);
>  	nworks = min(nworks, job->max_threads);
>  
>  	if (nworks == 1) {
> -- 
> 1.8.3.1
>