linux-kernel - Re: [PATCH] padata: Fix possible divide-by-0 panic in padata_mt

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Message-ID: <ZsQWV_j5zMuYWqvH@gondor.apana.org.au>
Date: Tue, 20 Aug 2024 12:06:47 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Daniel Jordan <daniel.m.jordan@...cle.com>
Cc: Waiman Long <longman@...hat.com>, steffen.klassert@...unet.com,
	akpm@...ux-foundation.org, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] padata: Fix possible divide-by-0 panic in
 padata_mt_helper()

On Mon, Aug 19, 2024 at 06:29:52PM -0400, Daniel Jordan wrote:
>
> The DIV_ROUND_UP approach reads a bit nicer to me, but I can imagine
> oddball cases where rounding up is undesirable (say, near-zero values
> for size, min_chunk, and align; padata_work_alloc_mt returns many fewer
> works than requested; and a single unit of work is very expensive) so
> that rounding up makes a bigger difference.  So, the way it now is seems
> ok.

In that case let's do the max ahead of the align check:

	ps.chunk_size = max(ps.chunk_size, 1ul);
	ps.chunk_size = roundup(ps.chunk_size, job->align);

If we do it after then it may come out unaligned (e.g., job->align = 8
and ps.chunk_size = 1).

Cheers,
-- 
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