Re: [PATCH v2 3/4] mm: hugetlb: Fix subpool usage leak on allocation failure

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 09 Sep 2026 14:49:28 -0700 Ackerley Tng via B4 Relay <devnull+ackerleytng.google.com@kernel.org> wrote:

> From: Ackerley Tng <ackerleytng@google.com>
> 
> When folio allocation fails early (e.g. buddy allocation failure or
> cgroup charging failure) and a reservation was not used (meaning an
> unreserved global page was needed), the subpool page acquired during the
> allocation attempt must still be returned.
> 
> Currently, the subpool cleanup error path only returns the page to the
> subpool if a reservation was used. If no reservation was used, it skips
> releasing the page back to the subpool, permanently leaking the subpool's
> used pages counter.
> 
> With subpools now always tracking used pages, always release the page
> back to the subpool whenever a subpool page was acquired.
> 
> Opportunistically rename the local variables tracking global reservations
> needed and global reservations returned. This clarifies the accounting:
> a value of zero for needed global reservations indicates an existing
> reservation satisfies the allocation, while a non-zero value indicates
> new global pages are required.
> 
> Adjust global reservations using the difference between reservations
> needed and reservations returned to properly handle races where concurrent
> threads interact with the same subpool.

This one conflicts with "mm/hugetlb: fix max-only subpool accounting on
alloc_hugetlb_folio failure". 
https://lore.kernel.org/20260428113037.88766-2-enderaoelyther@gmail.com.


> @@ -3074,13 +3074,10 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
>  	return folio;
>  
>  out_subpool_put:
> -	/*
> -	 * put page to subpool iff the quota of subpool's rsv_hpages is used
> -	 * during hugepage_subpool_get_pages.
> -	 */
> -	if (map_chg && !gbl_chg) {
> -		gbl_reserve = hugepage_subpool_put_pages(spool, 1);
> -		hugetlb_acct_memory(h, -gbl_reserve);
> +	if (map_chg) {
> +		long gbl_resv_put = hugepage_subpool_put_pages(spool, 1);
> +
> +		hugetlb_acct_memory(h, gbl_resv_get - gbl_resv_put);
>  	}
>  
>  out_end_reservation:

Here.

I presently have Zhao Li's patch staged in mm.git's
mm-hotfixes-unstable branch, awaiting review.

What to do?