From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with SMTP id 599C16B0190 for ; Sun, 14 Mar 2010 20:28:10 -0400 (EDT) Received: by pvg2 with SMTP id 2so348436pvg.14 for ; Sun, 14 Mar 2010 17:28:08 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <1268412087-13536-3-git-send-email-mel@csn.ul.ie> References: <1268412087-13536-1-git-send-email-mel@csn.ul.ie> <1268412087-13536-3-git-send-email-mel@csn.ul.ie> Date: Mon, 15 Mar 2010 09:28:08 +0900 Message-ID: <28c262361003141728g4aa40901hb040144c5a4aeeed@mail.gmail.com> Subject: Re: [PATCH 02/11] mm,migration: Do not try to migrate unmapped anonymous pages From: Minchan Kim Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org To: Mel Gorman Cc: Andrew Morton , Andrea Arcangeli , Christoph Lameter , Adam Litke , Avi Kivity , David Rientjes , KOSAKI Motohiro , Rik van Riel , linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: Hi, Mel. On Sat, Mar 13, 2010 at 1:41 AM, Mel Gorman wrote: > rmap_walk_anon() was triggering errors in memory compaction that looks li= ke > use-after-free errors in anon_vma. The problem appears to be that between > the page being isolated from the LRU and rcu_read_lock() being taken, the > mapcount of the page dropped to 0 and the anon_vma was freed. This patch > skips the migration of anon pages that are not mapped by anyone. > > Signed-off-by: Mel Gorman > Acked-by: Rik van Riel > --- > =C2=A0mm/migrate.c | =C2=A0 10 ++++++++++ > =C2=A01 files changed, 10 insertions(+), 0 deletions(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index 98eaaf2..3c491e3 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -602,6 +602,16 @@ static int unmap_and_move(new_page_t get_new_page, u= nsigned long private, > =C2=A0 =C2=A0 =C2=A0 =C2=A0 * just care Anon page here. > =C2=A0 =C2=A0 =C2=A0 =C2=A0 */ > =C2=A0 =C2=A0 =C2=A0 =C2=A0if (PageAnon(page)) { > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 /* > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0* If the page ha= s no mappings any more, just bail. An > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0* unmapped anon = page is likely to be freed soon but worse, > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0* it's possible = its anon_vma disappeared between when > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0* the page was i= solated and when we reached here while > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0* the RCU lock w= as not held > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0*/ > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 if (!page_mapcount(pag= e)) As looking code about mapcount of page, I got confused. I think mapcount of page is protected by pte lock. But I can't find pte lock in unmap_and_move. If I am right, what protects race between this condition check and rcu_read_lock? This patch makes race window very small but It can't remove race totally. I think I am missing something. Pz, point me out. :) > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0 goto uncharge; > + > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0rcu_read_lock(); > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0rcu_locked =3D 1; > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0anon_vma =3D page_= anon_vma(page); > -- > 1.6.5 > --=20 Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org