From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id 698866B0083 for ; Fri, 3 Jun 2011 12:37:28 -0400 (EDT) Received: from kpbe11.cbf.corp.google.com (kpbe11.cbf.corp.google.com [172.25.105.75]) by smtp-out.google.com with ESMTP id p53GbO76004769 for ; Fri, 3 Jun 2011 09:37:24 -0700 Received: from pxi7 (pxi7.prod.google.com [10.243.27.7]) by kpbe11.cbf.corp.google.com with ESMTP id p53Gav2O021263 (version=TLSv1/SSLv3 cipher=RC4-SHA bits=128 verify=NOT) for ; Fri, 3 Jun 2011 09:37:22 -0700 Received: by pxi7 with SMTP id 7so1195805pxi.16 for ; Fri, 03 Jun 2011 09:37:18 -0700 (PDT) Date: Fri, 3 Jun 2011 09:37:13 -0700 (PDT) From: Hugh Dickins Subject: Re: [PATCH] ksm: fix race between ksmd and exiting task In-Reply-To: <20110602173549.GL23047@sequoia.sous-sol.org> Message-ID: 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 Sender: owner-linux-mm@kvack.org List-ID: To: Chris Wright Cc: Andrea Righi , CAI Qian , Andrea Arcangeli , Rik van Riel , Mel Gorman , KAMEZAWA Hiroyuki , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton On Thu, 2 Jun 2011, 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. Remarkably similar to my patch: it must be good! But yours appears to be more popular - thanks, Chris. > > Reported-by: Andrea Righi > Cc: Hugh Dickins Acked-by: Hugh Dickins > Cc: Andrea Arcangeli > Signed-off-by: Chris Wright Cc: stable@kernel.org > --- > 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, 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org