Re: [PATCH] mm/sparse: fix preinited section_mem_map clobbering on failure path

David Hildenbrand (Arm)
2026-03-31T20:42:50Z

On 3/31/26 13:37, Muchun Song wrote:
> sparse_init_nid() is careful to leave alone every section whose vmemmap
> has already been set up by sparse_vmemmap_init_nid_early(); it only
> clears section_mem_map for the rest:
>
> if (!preinited_vmemmap_section(ms))
> ms->section_mem_map = 0;
>
> A leftover line after that conditional block
>
> ms->section_mem_map = 0;
>
> was supposed to be deleted but was missed in the failure path, causing the
> field to be overwritten for all sections when memory allocation fails,
> effectively destroying the pre-initialization check.
>
> Drop the stray assignment so that preinited sections retain their
> already valid state.
>
> Fixes: d65917c42373 ("mm/sparse: allow for alternate vmemmap section init at boot")
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
> mm/sparse.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index c2eb36bfb86d..3a14b733bf71 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -584,7 +584,6 @@ static void __init sparse_init_nid(int nid, unsigned long pnum_begin,
> ms = __nr_to_section(pnum);
> if (!preinited_vmemmap_section(ms))
> ms->section_mem_map = 0;
> - ms->section_mem_map = 0;

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

I have some cleanup patches lying around that cleanup that code heavily.
I think I get rid of this questionable "failed to allocate" case entirely.

--
Cheers,

David