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: <CAJuCfpEAfvFfFdNusJwPQGXM2sTMaB4RoEwjrUtwp1n3Afwk=Q@mail.gmail.com>
Date: Thu, 11 Sep 2025 14:51:25 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>
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 Thu, Sep 11, 2025 at 2:45 PM Shakeel Butt <shakeel.butt@...ux.dev> wrote:
>
> On Thu, Sep 11, 2025 at 01:12:11PM -0700, Suren Baghdasaryan wrote:
> > On Thu, Sep 11, 2025 at 1:01 PM Shakeel Butt <shakeel.butt@...ux.dev> wrote:
> > >
> > > 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?
> >
> > Pages released with release_pages() should have valid tags, so I
> > expect no warnings.
> >
>
> Oh so this is orthogonal to your first patch which is replacing
> __free_page with release_pages(). This non-compound high-order page is
> not an issue in the codepath vm_module_tags_populate(), correct?

Yes, these are independent fixes.