From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with ESMTP id 3DE206B00EB for ; Thu, 2 Jun 2011 13:36:23 -0400 (EDT) Date: Thu, 2 Jun 2011 10:35:49 -0700 From: Chris Wright 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> Sender: owner-linux-mm@kvack.org List-ID: 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 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, 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