Re: [PATCH] padata: Fix possible divide-by-0 panic in padata_mt_helper()
From: Kamlesh Gurudasani
Date: Wed Aug 21 2024 - 17:11:20 EST
Kamlesh Gurudasani <kamlesh@xxxxxx> writes:
> Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> writes:
>
>> 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.
> Thanks for consideration, Daniel. I'll send a patch.
Sent.
Just curious about one thing on line 495,
nworks = max(job->size / max(job->min_chunk, job->align), 1ul);
what happens if both min_chunk and align are 0.
cheers,
Kamlesh