linux-kernel - Re: [PATCHv6 17/17] mm/slab: Use compound_head() in page

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] [day] [month] [year] [list]

Message-ID: <0ecdd75e-ccd8-4217-a409-51da756ff1fe@kernel.org>
Date: Fri, 6 Feb 2026 11:42:10 +0100
From: "David Hildenbrand (Arm)" <david@...nel.org>
To: Kiryl Shutsemau <kas@...nel.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Muchun Song <muchun.song@...ux.dev>, Matthew Wilcox <willy@...radead.org>,
 Usama Arif <usamaarif642@...il.com>, Frank van der Linden <fvdl@...gle.com>
Cc: Oscar Salvador <osalvador@...e.de>, Mike Rapoport <rppt@...nel.org>,
 Vlastimil Babka <vbabka@...e.cz>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Zi Yan <ziy@...dia.com>,
 Baoquan He <bhe@...hat.com>, Michal Hocko <mhocko@...e.com>,
 Johannes Weiner <hannes@...xchg.org>, Jonathan Corbet <corbet@....net>,
 Huacai Chen <chenhuacai@...nel.org>, WANG Xuerui <kernel@...0n.name>,
 Palmer Dabbelt <palmer@...belt.com>, Paul Walmsley
 <paul.walmsley@...ive.com>, Albert Ou <aou@...s.berkeley.edu>,
 Alexandre Ghiti <alex@...ti.fr>, kernel-team@...a.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 loongarch@...ts.linux.dev, linux-riscv@...ts.infradead.org
Subject: Re: [PATCHv6 17/17] mm/slab: Use compound_head() in page_slab()

On 2/2/26 16:56, Kiryl Shutsemau wrote:
> page_slab() contained an open-coded implementation of compound_head().
> 
> Replace the duplicated code with a direct call to compound_head().
> 
> Signed-off-by: Kiryl Shutsemau <kas@...nel.org>
> 
> ---
> 
> I am not sure if this open-coded version is intentional and required for
> memdesc transition. Drop the patch if it is.

commit 2bcd3800f2da1be13b972858f63c66d035b1ec6d
Author: Matthew Wilcox (Oracle) <willy@...radead.org>
Date:   Thu Nov 13 00:09:15 2025 +0000

     slab: Reimplement page_slab()
     
     In order to separate slabs from folios, we need to convert from any page
     in a slab to the slab directly without going through a page to folio
     conversion first.

     Up to this point, page_slab() has followed the example of other memdesc
     converters (page_folio(), page_ptdesc() etc) and just cast the pointer
     to the requested type, regardless of whether the pointer is actually a
     pointer to the correct type or not.
     
     That changes with this commit; we check that the page actually belongs
     to a slab and return NULL if it does not.  Other memdesc converters will
     adopt this convention in future.


I think using compound_head() is fine. For memdescs the function has to be changed to
lookup the memdesc either way, and not go through the head page.

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

-- 
Cheers,

David