Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753489Ab1FBQtX (ORCPT ); Thu, 2 Jun 2011 12:49:23 -0400 Received: from sous-sol.org ([216.99.217.87]:39469 "EHLO sequoia.sous-sol.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751902Ab1FBQtW (ORCPT ); Thu, 2 Jun 2011 12:49:22 -0400 Date: Thu, 2 Jun 2011 09:48:41 -0700 From: Chris Wright To: Andrea Righi Cc: CAI Qian , Hugh Dickins , Andrea Arcangeli , Rik van Riel , Chris Wright , Mel Gorman , Izik Eidus , KAMEZAWA Hiroyuki , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton Subject: Re: [BUG 3.0.0-rc1] ksm: NULL pointer dereference in ksm_do_scan() Message-ID: <20110602164841.GK23047@sequoia.sous-sol.org> References: <20110601222032.GA2858@thinkpad> <2144269697.363041.1306998593180.JavaMail.root@zmail06.collab.prod.int.phx2.redhat.com> <20110602141927.GA2011@thinkpad> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110602141927.GA2011@thinkpad> 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: 1175 Lines: 36 * Andrea Righi (andrea@betterlinux.com) wrote: > mmh.. I can reproduce the bug also with the standard ubuntu (11.04) > kernel. Could you post your .config? Andrea (Righi), can you tell me if this WARN fires? This looks like a pure race between removing from list and checking list, i.e. insufficient locking. 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_) diff --git a/mm/ksm.c b/mm/ksm.c index 942dfc7..ab79a92 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -1301,6 +1301,7 @@ 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); + WARN_ON(slot == &ksm_mm_head); 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/