On 8/10/24 21:45, Herbert Xu wrote:
On Sat, Aug 10, 2024 at 09:30:25PM -0400, Waiman Long wrote:
On 8/10/24 00:05, Herbert Xu wrote:
Waiman Long <longman@xxxxxxxxxx> 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.
Unless I'm missing something chunk_size cannot be zero before the
division because that's the first thing we check upon entry into
this function.
chunk_size is initialized as
ps.chunk_size = job->size / (ps.nworks * load_balance_factor);
chunk_size will be 0 if job->size < (ps.nworks * load_balance_factor).
If min_chunk is 0, chunk_size will remain 0.
After looking at the dump file when the crash happen at
padata_mt_helper(). I had determined that ps->chunk_size was indeed 0
which caused the divide-by-0 panic. I actually got 2 different bug
reports of this div-by-0 panic, one with a debug and another one with a
non-debug kernel.
Cheers,
Longman
