From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: Nick Piggin <npiggin@suse.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
Andrea Arcangeli <aarcange@redhat.com>,
Avi Kivity <avi@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
Rik van Riel <riel@redhat.com>, Ingo Molnar <mingo@elte.hu>,
akpm@linux-foundation.org,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
David Miller <davem@davemloft.net>,
Hugh Dickins <hugh.dickins@tiscali.co.uk>,
Mel Gorman <mel@csn.ul.ie>
Subject: Re: [PATCH 02/13] mm: Revalidate anon_vma in page_lock_anon_vma()
Date: Fri, 9 Apr 2010 13:56:57 +0900 [thread overview]
Message-ID: <20100409135657.8f234c9a.kamezawa.hiroyu@jp.fujitsu.com> (raw)
In-Reply-To: <20100409031641.GG5683@laptop>
On Fri, 9 Apr 2010 13:16:41 +1000
Nick Piggin <npiggin@suse.de> wrote:
> On Thu, Apr 08, 2010 at 09:17:39PM +0200, Peter Zijlstra wrote:
> > There is nothing preventing the anon_vma from being detached while we
> > are spinning to acquire the lock. Most (all?) current users end up
> > calling something like vma_address(page, vma) on it, which has a
> > fairly good chance of weeding out wonky vmas.
> >
> > However suppose the anon_vma got freed and re-used while we were
> > waiting to acquire the lock, and the new anon_vma fits with the
> > page->index (because that is the only thing vma_address() uses to
> > determine if the page fits in a particular vma, we could end up
> > traversing faulty anon_vma chains.
> >
> > Close this hole for good by re-validating that page->mapping still
> > holds the very same anon_vma pointer after we acquire the lock, if not
> > be utterly paranoid and retry the whole operation (which will very
> > likely bail, because it's unlikely the page got attached to a different
> > anon_vma in the meantime).
>
> Hm, looks like a bugfix? How was this supposed to be safe?
>
IIUC.
Before Rik's change to anon_vma, once page->mapping is set as anon_vma | 0x1,
it's not modified until the page is freed.
After the patch, do_wp_page() overwrite page->mapping when it reuse existing
page.
==
static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long address, pte_t *page_table, pmd_t *pmd,
spinlock_t *ptl, pte_t orig_pte)
{
....
if (PageAnon(old_page) && !PageKsm(old_page)) {
if (!trylock_page(old_page)) {
page_cache_get(old_page);
....
reuse = reuse_swap_page(old_page);
if (reuse)
/*
* The page is all ours. Move it to our anon_vma so
* the rmap code will not search our parent or siblings.
* Protected against the rmap code by the page lock.
*/
page_move_anon_rmap(old_page, vma, address); ----(*)
}
===
(*) is new.
Then, this new check makes sense in the current kernel.
>
> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> > Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
> > Cc: Linus Torvalds <torvalds@linux-foundation.org>
> > ---
> > mm/rmap.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > Index: linux-2.6/mm/rmap.c
> > ===================================================================
> > --- linux-2.6.orig/mm/rmap.c
> > +++ linux-2.6/mm/rmap.c
> > @@ -294,6 +294,7 @@ struct anon_vma *page_lock_anon_vma(stru
> > unsigned long anon_mapping;
> >
> > rcu_read_lock();
> > +again:
> > anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping);
> > if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
> > goto out;
> > @@ -302,6 +303,12 @@ struct anon_vma *page_lock_anon_vma(stru
> >
> > anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
> > spin_lock(&anon_vma->lock);
> > +
> > + if (page_rmapping(page) != anon_vma) {
>
> very unlikely()?
>
I think so.
Thanks,
-Kame
next prev parent reply other threads:[~2010-04-09 5:01 UTC|newest]
Thread overview: 96+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-04-08 19:17 [PATCH 00/13] mm: preemptibility -v2 Peter Zijlstra
2010-04-08 19:17 ` [PATCH 01/13] powerpc: Add rcu_read_lock() to gup_fast() implementation Peter Zijlstra
2010-04-08 20:31 ` Rik van Riel
2010-04-09 3:11 ` Nick Piggin
2010-04-13 1:05 ` Benjamin Herrenschmidt
2010-04-13 3:43 ` Paul E. McKenney
2010-04-14 13:51 ` Peter Zijlstra
2010-04-15 14:28 ` Paul E. McKenney
2010-04-16 6:54 ` Benjamin Herrenschmidt
2010-04-16 13:43 ` Paul E. McKenney
2010-04-16 23:25 ` Benjamin Herrenschmidt
2010-04-16 13:51 ` Peter Zijlstra
2010-04-16 14:17 ` Paul E. McKenney
2010-04-16 14:23 ` Peter Zijlstra
2010-04-16 14:32 ` Paul E. McKenney
2010-04-16 14:56 ` Peter Zijlstra
2010-04-16 15:09 ` Paul E. McKenney
2010-04-16 15:14 ` Peter Zijlstra
2010-04-16 16:45 ` Paul E. McKenney
2010-04-16 19:37 ` Peter Zijlstra
2010-04-16 20:28 ` Paul E. McKenney
2010-04-18 3:06 ` James Bottomley
2010-04-18 13:55 ` Paul E. McKenney
2010-04-18 18:55 ` James Bottomley
2010-04-16 6:51 ` Benjamin Herrenschmidt
2010-04-16 8:18 ` Nick Piggin
2010-04-16 8:29 ` Benjamin Herrenschmidt
2010-04-16 9:22 ` Nick Piggin
2010-04-08 19:17 ` [PATCH 02/13] mm: Revalidate anon_vma in page_lock_anon_vma() Peter Zijlstra
2010-04-08 20:50 ` Rik van Riel
2010-04-08 21:20 ` Andrew Morton
2010-04-08 21:54 ` Peter Zijlstra
2010-04-09 2:19 ` KOSAKI Motohiro
2010-04-09 2:19 ` Minchan Kim
2010-04-09 3:16 ` Nick Piggin
2010-04-09 4:56 ` KAMEZAWA Hiroyuki [this message]
2010-04-09 6:34 ` KOSAKI Motohiro
2010-04-09 6:47 ` KAMEZAWA Hiroyuki
2010-04-09 7:29 ` KOSAKI Motohiro
2010-04-09 7:57 ` KAMEZAWA Hiroyuki
2010-04-09 8:03 ` KAMEZAWA Hiroyuki
2010-04-09 8:24 ` KAMEZAWA Hiroyuki
2010-04-09 8:01 ` Minchan Kim
2010-04-09 8:17 ` KOSAKI Motohiro
2010-04-09 14:41 ` mlock and pageout race? Minchan Kim
2010-04-09 8:44 ` [PATCH 02/13] mm: Revalidate anon_vma in page_lock_anon_vma() Peter Zijlstra
2010-05-24 19:32 ` Andrew Morton
2010-05-25 9:01 ` Peter Zijlstra
2010-04-09 12:57 ` Peter Zijlstra
2010-04-08 19:17 ` [PATCH 03/13] x86: Remove last traces of quicklist usage Peter Zijlstra
2010-04-08 20:51 ` Rik van Riel
2010-04-08 19:17 ` [PATCH 04/13] mm: Move anon_vma ref out from under CONFIG_KSM Peter Zijlstra
2010-04-09 12:35 ` Rik van Riel
2010-04-08 19:17 ` [PATCH 05/13] mm: Make use of the anon_vma ref count Peter Zijlstra
2010-04-09 7:04 ` Christian Ehrhardt
2010-04-09 9:57 ` Peter Zijlstra
2010-04-08 19:17 ` [PATCH 06/13] mm: Preemptible mmu_gather Peter Zijlstra
2010-04-09 3:25 ` Nick Piggin
2010-04-09 8:18 ` Peter Zijlstra
2010-04-09 20:36 ` Peter Zijlstra
2010-04-19 19:16 ` Peter Zijlstra
2010-04-08 19:17 ` [PATCH 07/13] powerpc: " Peter Zijlstra
2010-04-09 4:07 ` Nick Piggin
2010-04-09 8:14 ` Peter Zijlstra
2010-04-09 8:46 ` Nick Piggin
2010-04-09 9:22 ` Peter Zijlstra
2010-04-13 2:06 ` Benjamin Herrenschmidt
2010-04-13 1:56 ` Benjamin Herrenschmidt
2010-04-13 1:23 ` Benjamin Herrenschmidt
2010-04-13 10:22 ` Peter Zijlstra
2010-04-14 13:34 ` Peter Zijlstra
2010-04-14 13:51 ` Peter Zijlstra
2010-04-08 19:17 ` [PATCH 08/13] sparc: " Peter Zijlstra
2010-04-08 19:17 ` [PATCH 09/13] mm, powerpc: Move the RCU page-table freeing into generic code Peter Zijlstra
2010-04-09 3:35 ` Nick Piggin
2010-04-09 8:08 ` Peter Zijlstra
2010-04-08 19:17 ` [PATCH 10/13] lockdep, mutex: Provide mutex_lock_nest_lock Peter Zijlstra
2010-04-09 15:36 ` Rik van Riel
2010-04-08 19:17 ` [PATCH 11/13] mutex: Provide mutex_is_contended Peter Zijlstra
2010-04-09 15:37 ` Rik van Riel
2010-04-08 19:17 ` [PATCH 12/13] mm: Convert i_mmap_lock and anon_vma->lock to mutexes Peter Zijlstra
2010-04-08 19:17 ` [PATCH 13/13] mm: Optimize page_lock_anon_vma Peter Zijlstra
2010-04-08 22:18 ` Paul E. McKenney
2010-04-09 8:35 ` Peter Zijlstra
2010-04-09 19:22 ` Paul E. McKenney
2010-04-08 20:29 ` [PATCH 00/13] mm: preemptibility -v2 David Miller
2010-04-08 20:35 ` Peter Zijlstra
2010-04-09 1:00 ` David Miller
2010-04-09 4:14 ` Nick Piggin
2010-04-09 8:35 ` Peter Zijlstra
2010-04-09 8:50 ` Nick Piggin
2010-04-09 8:58 ` Peter Zijlstra
2010-04-09 8:58 ` Martin Schwidefsky
2010-04-09 9:53 ` Peter Zijlstra
2010-04-09 9:03 ` David Howells
2010-04-09 9:22 ` Peter Zijlstra
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20100409135657.8f234c9a.kamezawa.hiroyu@jp.fujitsu.com \
--to=kamezawa.hiroyu@jp.fujitsu.com \
--cc=a.p.zijlstra@chello.nl \
--cc=aarcange@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=avi@redhat.com \
--cc=benh@kernel.crashing.org \
--cc=davem@davemloft.net \
--cc=hugh.dickins@tiscali.co.uk \
--cc=linux-arch@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mel@csn.ul.ie \
--cc=mingo@elte.hu \
--cc=npiggin@suse.de \
--cc=riel@redhat.com \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).