linux-kernel - Re: [PATCH v5 20/37] mm: fix non-compound multi-order memory accounting in __free

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: <CAJuCfpFf2xrCA_Rq_-e5HsDMqeS87p0b28PkK+wgWco17mxyDQ@mail.gmail.com>
Date: Wed, 13 Mar 2024 15:31:18 +0000
From: Suren Baghdasaryan <surenb@...gle.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: akpm@...ux-foundation.org, kent.overstreet@...ux.dev, mhocko@...e.com, 
	vbabka@...e.cz, hannes@...xchg.org, roman.gushchin@...ux.dev, mgorman@...e.de, 
	dave@...olabs.net, liam.howlett@...cle.com, 
	penguin-kernel@...ove.sakura.ne.jp, corbet@....net, void@...ifault.com, 
	peterz@...radead.org, juri.lelli@...hat.com, catalin.marinas@....com, 
	will@...nel.org, arnd@...db.de, tglx@...utronix.de, mingo@...hat.com, 
	dave.hansen@...ux.intel.com, x86@...nel.org, peterx@...hat.com, 
	david@...hat.com, axboe@...nel.dk, mcgrof@...nel.org, masahiroy@...nel.org, 
	nathan@...nel.org, dennis@...nel.org, jhubbard@...dia.com, tj@...nel.org, 
	muchun.song@...ux.dev, rppt@...nel.org, paulmck@...nel.org, 
	pasha.tatashin@...een.com, yosryahmed@...gle.com, yuzhao@...gle.com, 
	dhowells@...hat.com, hughd@...gle.com, andreyknvl@...il.com, 
	keescook@...omium.org, ndesaulniers@...gle.com, vvvvvv@...gle.com, 
	gregkh@...uxfoundation.org, ebiggers@...gle.com, ytcoode@...il.com, 
	vincent.guittot@...aro.org, dietmar.eggemann@....com, rostedt@...dmis.org, 
	bsegall@...gle.com, bristot@...hat.com, vschneid@...hat.com, cl@...ux.com, 
	penberg@...nel.org, iamjoonsoo.kim@....com, 42.hyeyoo@...il.com, 
	glider@...gle.com, elver@...gle.com, dvyukov@...gle.com, shakeelb@...gle.com, 
	songmuchun@...edance.com, jbaron@...mai.com, aliceryhl@...gle.com, 
	rientjes@...gle.com, minchan@...gle.com, kaleshsingh@...gle.com, 
	kernel-team@...roid.com, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, iommu@...ts.linux.dev, 
	linux-arch@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, 
	linux-modules@...r.kernel.org, kasan-dev@...glegroups.com, 
	cgroups@...r.kernel.org
Subject: Re: [PATCH v5 20/37] mm: fix non-compound multi-order memory
 accounting in __free_pages

On Wed, Mar 13, 2024 at 3:04 PM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Wed, Mar 06, 2024 at 10:24:18AM -0800, Suren Baghdasaryan wrote:
> > When a non-compound multi-order page is freed, it is possible that a
> > speculative reference keeps the page pinned. In this case we free all
> > pages except for the first page, which will be freed later by the last
> > put_page(). However put_page() ignores the order of the page being freed,
> > treating it as a 0-order page. This creates a memory accounting imbalance
> > because the pages freed in __free_pages() do not have their own alloc_tag
> > and their memory was accounted to the first page. To fix this the first
> > page should adjust its allocation size counter when "tail" pages are freed.
>
> It's not "ignored".  It's not available!
>
> Better wording:
>
> However the page passed to put_page() is indisinguishable from an
> order-0 page, so it cannot do the accounting, just as it cannot free
> the subsequent pages.  Do the accounting here, where we free the pages.
>
> (I'm sure further improvements are possible)
>
> > +static inline void pgalloc_tag_sub_bytes(struct alloc_tag *tag, unsigned int order)
> > +{
> > +     if (mem_alloc_profiling_enabled() && tag)
> > +             this_cpu_sub(tag->counters->bytes, PAGE_SIZE << order);
> > +}
>
> This is a terribly named function.  And it's not even good for what we
> want to use it for.
>
> static inline void pgalloc_tag_sub_pages(struct alloc_tag *tag, unsigned int nr)
> {
>         if (mem_alloc_profiling_enabled() && tag)
>                 this_cpu_sub(tag->counters->bytes, PAGE_SIZE * nr);
> }
>
> > +++ b/mm/page_alloc.c
> > @@ -4697,12 +4697,21 @@ void __free_pages(struct page *page, unsigned int order)
> >  {
> >       /* get PageHead before we drop reference */
> >       int head = PageHead(page);
> > +     struct alloc_tag *tag = pgalloc_tag_get(page);
> >
> >       if (put_page_testzero(page))
> >               free_the_page(page, order);
> >       else if (!head)
> > -             while (order-- > 0)
> > +             while (order-- > 0) {
> >                       free_the_page(page + (1 << order), order);
> > +                     /*
> > +                      * non-compound multi-order page accounts all allocations
> > +                      * to the first page (just like compound one), therefore
> > +                      * we need to adjust the allocation size of the first
> > +                      * page as its order is ignored when put_page() frees it.
> > +                      */
> > +                     pgalloc_tag_sub_bytes(tag, order);
>
> -       else if (!head
> +       else if (!head) {
> +               pgalloc_tag_sub_pages(1 << order - 1);
>                 while (order-- > 0)
>                         free_the_page(page + (1 << order), order);
> +       }
>
> It doesn't need a comment, it's obvious what you're doing.

All suggestions seem fine to me. I'll adjust the next version accordingly.
Thanks for reviewing and the feedback!

>