linux-kernel - Re: [PATCH] mm: use a irq-safe __mod_zone_page_state in mlocked_vma

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]

Date:	Fri, 9 May 2014 12:54:26 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jianyu Zhan <nasa4836@...il.com>
Cc:	cl@...ux.com, mhocko@...e.cz, hannes@...xchg.org, riel@...hat.com,
	minchan@...nel.org, zhangyanfei@...fujitsu.com,
	hanpt@...ux.vnet.ibm.com, sasha.levin@...cle.com, oleg@...hat.com,
	fabf@...net.be, mgorman@...e.de, aarcange@...hat.com,
	cldu@...vell.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: use a irq-safe __mod_zone_page_state in
 mlocked_vma_newpage()

On Sat, 10 May 2014 00:16:48 +0800 Jianyu Zhan <nasa4836@...il.com> wrote:

> mlocked_vma_newpage() is only called in fault path by
> page_add_new_anon_rmap(), which is called on a *new* page.
> And such page is initially only visible via the pagetables, and the
> pte is locked while calling page_add_new_anon_rmap(), so we need not
> use an irq-safe mod_zone_page_state() here, using a light-weight version
> __mod_zone_page_state() would be OK.
> 
> ...
>
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -196,7 +196,7 @@ static inline int mlocked_vma_newpage(struct vm_area_struct *vma,
>  		return 0;
>  
>  	if (!TestSetPageMlocked(page)) {
> -		mod_zone_page_state(page_zone(page), NR_MLOCK,
> +		__mod_zone_page_state(page_zone(page), NR_MLOCK,
>  				    hpage_nr_pages(page));
>  		count_vm_event(UNEVICTABLE_PGMLOCKED);
>  	}

The comment over __mod_zone_page_state() says "For use when we know
that interrupts are disabled".  But that is not the case here.

Please fix this up, probably by altering the __mod_zone_page_state()
documentation.


Your proposed change to (the very poorly named) mlocked_vma_newpage()
makes that function more dangerous - people might add new callsites
without knowing that they're adding races.  This risk can be reduced by

a) adding documentation explaining why __mod_zone_page_state() is
   used and why it is safe and

b) moving mlocked_vma_newpage() out of internal.h and placing it in
   mm/rmap.c immediately before page_add_new_anon_rmap().  Or, probably
   better, by removing mlocked_vma_newpage() altogether and open-coding
   its logic into page_add_new_anon_rmap().


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/