Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752692Ab1FCQh0 (ORCPT ); Fri, 3 Jun 2011 12:37:26 -0400 Received: from smtp-out.google.com ([74.125.121.67]:62943 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752329Ab1FCQhY (ORCPT ); Fri, 3 Jun 2011 12:37:24 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=date:from:x-x-sender:to:cc:subject:in-reply-to:message-id :references:user-agent:mime-version:content-type; b=leD/jMTow4ogO5wy8nnsnB042W05pR/aNPERjynJkOzHiMTdcyK1U3GQcWtw1y/TSm B0BdMg0/2Omod3f8S/TQ== Date: Fri, 3 Jun 2011 09:37:13 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@sister.anvils 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 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> User-Agent: Alpine 2.00 (LSU 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1636 Lines: 54 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 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/