Re: [PATCH] padata: Fix possible divide-by-0 panic in padata_mt_helper()

[Waiman Long <longman@redhat.com>]

On 8/10/24 00:05, Herbert Xu wrote:
> Waiman Long <longman@redhat.com> wrote:
>> diff --git a/kernel/padata.c b/kernel/padata.c
>> index 53f4bc912712..0fa6c2895460 100644
>> --- a/kernel/padata.c
>> +++ b/kernel/padata.c
>> @@ -517,6 +517,13 @@ void __init padata_do_multithreaded(struct padata_mt_job *job)
>>         ps.chunk_size = max(ps.chunk_size, job->min_chunk);
>>         ps.chunk_size = roundup(ps.chunk_size, job->align);
>>
>> +       /*
>> +        * chunk_size can be 0 if the caller sets min_chunk to 0. So force it
>> +        * to at least 1 to prevent divide-by-0 panic in padata_mt_helper().`
>> +        */
>> +       if (!ps.chunk_size)
>> +               ps.chunk_size = 1U;
> Perhaps change the first ps.chunk_size assignment to use DIV_ROUND_UP
> instead?

I think DIV_ROUND_UP() will exactly the same problem that if chunk_size 
is 0, you still got a 0 result. round_up() only if the 2nd argument is a 
power of 2 while with DIV_ROUND_UP(), the second argument can be any 
number except 0.

Cheers,
Longman