Re: [PATCH v2] mm/hugetlb: Fix null nodemask in alloc_fresh_hugetlb_folio

[Andrew Morton]

On Sat,  4 Jul 2026 17:49:30 +0000 Sourav Panda <souravpanda@xxxxxxxxxx> wrote:

> alloc_buddy_hugetlb_folio_with_mpol() can pass a NULL nodemask to
> alloc_fresh_hugetlb_folio() as a fallback to allocate from all
> nodes. If order is gigantic, alloc_fresh_hugetlb_folio() propagates
> the NULL nodemask down to hugetlb_cma_alloc_frozen_folio() which blindly
> dereferences it in for_each_node_mask(), leading to a null pointer
> dereference.
> 
> Similarly, if the CMA allocation fails, the fallback
> alloc_contig_frozen_pages() is also called with a NULL nodemask,
> which may cause issues.
> 
> Fix this by explicitly checking if nodemask is NULL in
> alloc_fresh_hugetlb_folio() and defaulting to
> cpuset_current_mems_allowed. This ensures that both the CMA and
> contiguous allocators receive a valid nodemask.
> 
> Additionally, this patch adds a missing node_isset(nid, *nodemask) check
> in hugetlb_cma_alloc_frozen_folio() to ensure the initial node allocation
> attempt respects the memory policy.

Thanks, bu the changelog still doesn't explain the userspace visible
effects of the bug :(  Important when proposing a cc:stable bugfix.

So can you please condense and include the info you sent in reply to
my v1 question?


Also, Sashiko is saying stuff, as usual:
	https://sashiko.dev/#/patchset/20260704174930.2885785-1-souravpanda@xxxxxxxxxx