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

[David Hildenbrand (Arm)]

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@xxxxxxxxxxxxx>
> ---
>  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@xxxxxxxxxx>

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