Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754584Ab1FBUMm (ORCPT ); Thu, 2 Jun 2011 16:12:42 -0400 Received: from mail.betterlinux.com ([199.58.199.50]:52784 "EHLO mail.betterlinux.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753262Ab1FBUMm (ORCPT ); Thu, 2 Jun 2011 16:12:42 -0400 Date: Thu, 2 Jun 2011 22:12:36 +0200 From: Andrea Righi To: Chris Wright Cc: CAI Qian , Hugh Dickins , Andrea Arcangeli , Rik van Riel , Mel Gorman , Izik Eidus , KAMEZAWA Hiroyuki , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton Subject: Re: [PATCH] ksm: fix race between ksmd and exiting task Message-ID: <20110602201236.GB4114@thinkpad> References: <20110601222032.GA2858@thinkpad> <2144269697.363041.1306998593180.JavaMail.root@zmail06.collab.prod.int.phx2.redhat.com> <20110602141927.GA2011@thinkpad> <20110602164841.GK23047@sequoia.sous-sol.org> <20110602173549.GL23047@sequoia.sous-sol.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110602173549.GL23047@sequoia.sous-sol.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1581 Lines: 48 On Thu, Jun 02, 2011 at 10:35:49AM -0700, Chris Wright wrote: > Andrea Righi reported a case where an exiting task can race against > ksmd. > > ksm_scan.mm_slot == the only registered mm > CPU 1 (bug program) CPU 2 (ksmd) > list_empty() is false > lock > ksm_scan.mm_slot > list_del > unlock > slot == &ksm_mm_head (but list is now empty_) > > Close this race by revalidating that the new slot is not simply the list > head again. I confirm this fixes the problem on my side. Tested-by: Andrea Righi > > Reported-by: Andrea Righi > Cc: Hugh Dickins > Cc: Andrea Arcangeli > Signed-off-by: Chris Wright > --- > mm/ksm.c | 3 +++ > 1 files changed, 3 insertions(+), 0 deletions(-) > > diff --git a/mm/ksm.c b/mm/ksm.c > index 942dfc7..0373ce4 100644 > --- a/mm/ksm.c > +++ b/mm/ksm.c > @@ -1301,6 +1301,9 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page) > slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list); > ksm_scan.mm_slot = slot; > spin_unlock(&ksm_mmlist_lock); > + /* We raced against exit of last slot on the list */ > + if (slot == &ksm_mm_head) > + return NULL; > next_mm: > ksm_scan.address = 0; > ksm_scan.rmap_list = &slot->rmap_list; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/