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

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Message-ID: <3kexyvcrc5pxp4cqlgt7tvdbo3hbt225w76kczjdlzwitpeuto@addhycc4evbe>
Date: Tue, 20 Aug 2024 17:24:30 -0400
From: Daniel Jordan <daniel.m.jordan@...cle.com>
To: Herbert Xu <herbert@...dor.apana.org.au>
Cc: Waiman Long <longman@...hat.com>, steffen.klassert@...unet.com,
        akpm@...ux-foundation.org, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org, Kamlesh Gurudasani <kamlesh@...com>
Subject: Re: [PATCH] padata: Fix possible divide-by-0 panic in
 padata_mt_helper()

On Tue, Aug 20, 2024 at 12:06:47PM GMT, Herbert Xu wrote:
> 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).

Sure, I think Kamlesh was the first to suggest max, so maybe Kamlesh
would like to make the change.  I'll send a patch otherwise.