linux-kernel - Re: [PATCH 3/3] alloc_tag: avoid warnings when freeing non-compound "tail" pages

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <zxbgiqf4d3nlww2xxoea7rud3q4oj2osk657xnhu6r7du4lf3p@es7mqt7joo7b>
Date: Thu, 11 Sep 2025 13:01:18 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: akpm@...ux-foundation.org, kent.overstreet@...ux.dev, vbabka@...e.cz, 
	mhocko@...e.com, jackmanb@...gle.com, hannes@...xchg.org, ziy@...dia.com, 
	usamaarif642@...il.com, 00107082@....com, pasha.tatashin@...een.com, 
	souravpanda@...gle.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] alloc_tag: avoid warnings when freeing non-compound
 "tail" pages

On Tue, Sep 09, 2025 at 04:34:09PM -0700, Suren Baghdasaryan wrote:
> When freeing "tail" pages of a non-compount high-order page, we properly
> subtract the allocation tag counters, however later when these pages are
> released, alloc_tag_sub() will issue warnings because tags for these pages
> are NULL.
> This issue was originally anticipated by Vlastimil in his review [1] and
> then recently reported by David.
> Prevent warnings by marking the tags empty.
> 
> [1] https://lore.kernel.org/all/6db0f0c8-81cb-4d04-9560-ba73d63db4b8@suse.cz/
> 
> Suggested-by: David Wang <00107082@....com>
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> ---
>  mm/page_alloc.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 1760346bbd24..d21a411e807e 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5240,9 +5240,16 @@ static void ___free_pages(struct page *page, unsigned int order,
>  		__free_frozen_pages(page, order, fpi_flags);
>  	else if (!head) {
>  		pgalloc_tag_sub_pages(tag, (1 << order) - 1);
> -		while (order-- > 0)
> +		while (order-- > 0) {
> +			/*
> +			 * The "tail" pages of this non-compound high-order
> +			 * page will have no code tags, so to avoid warnings
> +			 * mark them as empty.
> +			 */
> +			clear_page_tag_ref(page + (1 << order));

Do we need something similar for the release_pages() code path or is it
happening already?

>  			__free_frozen_pages(page + (1 << order), order,
>  					    fpi_flags);
> +		}
>  	}
>  }
>  
> -- 
> 2.51.0.384.g4c02a37b29-goog
>