Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753837Ab1FBRg1 (ORCPT ); Thu, 2 Jun 2011 13:36:27 -0400 Received: from sous-sol.org ([216.99.217.87]:43545 "EHLO sequoia.sous-sol.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753148Ab1FBRg0 (ORCPT ); Thu, 2 Jun 2011 13:36:26 -0400 Date: Thu, 2 Jun 2011 10:35:49 -0700 From: Chris Wright To: Chris Wright Cc: Andrea Righi , 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: [PATCH] ksm: fix race between ksmd and exiting task Message-ID: <20110602173549.GL23047@sequoia.sous-sol.org> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110602164841.GK23047@sequoia.sous-sol.org> User-Agent: Mutt/1.5.20 (2009-08-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1348 Lines: 42 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. 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/