From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756488AbZICV3L (ORCPT ); Thu, 3 Sep 2009 17:29:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756443AbZICV3K (ORCPT ); Thu, 3 Sep 2009 17:29:10 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:57037 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756380AbZICV3K (ORCPT ); Thu, 3 Sep 2009 17:29:10 -0400 Date: Thu, 3 Sep 2009 14:28:36 -0700 From: Andrew Morton To: KAMEZAWA Hiroyuki Cc: linux-kernel@vger.kernel.org, jens.axboe@oracle.com, linux-mm@kvack.org, Mel Gorman Subject: Re: [mmotm][BUG] lockdep warning block I/O (Was Re: mmotm 2009-08-27-16-51 uploaded Message-Id: <20090903142836.fef35b23.akpm@linux-foundation.org> In-Reply-To: <20090901180717.f707c58f.kamezawa.hiroyu@jp.fujitsu.com> References: <200908272355.n7RNtghC019990@imap1.linux-foundation.org> <20090901180717.f707c58f.kamezawa.hiroyu@jp.fujitsu.com> X-Mailer: Sylpheed version 2.2.4 (GTK+ 2.8.20; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 1 Sep 2009 18:07:17 +0900 KAMEZAWA Hiroyuki wrote: > > Here is mmont-Aug27's lockdep wanring. This was printed out when oom-kill happens. > I'm sorry if already fixed. My life's project is to hunt down the guy who invented mail client wordwrapping, set him on fire then dance on his ashes. > = > Sep 1 18:01:16 localhost kernel: [ 3012.503035] ====================================================== > Sep 1 18:01:16 localhost kernel: [ 3012.503039] [ INFO: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected ] > Sep 1 18:01:16 localhost kernel: [ 3012.503042] 2.6.31-rc7-mm1 #3 > Sep 1 18:01:16 localhost kernel: [ 3012.503049] ------------------------------------------------------ > Sep 1 18:01:16 localhost kernel: [ 3012.503052] kblockd/7/350 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire: > Sep 1 18:01:16 localhost kernel: [ 3012.503058] (bdev_lock){+.+...}, at: [] nr_blockdev_pages+0x1 > 7/0x80 > Sep 1 18:01:16 localhost kernel: [ 3012.503069] > Sep 1 18:01:16 localhost kernel: [ 3012.503070] and this task is already holding: > Sep 1 18:01:16 localhost kernel: [ 3012.503075] (&q->__queue_lock){..-.-.}, at: [] cfq_kick_queue > +0x28/0x50 > Sep 1 18:01:16 localhost kernel: [ 3012.503083] which would create a new lock dependency: > Sep 1 18:01:16 localhost kernel: [ 3012.503087] (&q->__queue_lock){..-.-.} -> (bdev_lock){+.+...} > Sep 1 18:01:16 localhost kernel: [ 3012.503100] I'd say the core problem here is that __alloc_pages_slowpath() is calling show_mem(). Because show_mem() is a "high level" function which takes "high level" locks. ie: bdev_lock. It's inappropriate that alloc_pages() is assuming that it is safe to call show_mem() from all contexts in which alloc_pages() might be called. That show_mem() call has been there since 2005, so I don't know what caused this to be revealed now. It's not at all a serious bug and the chances of us deadlocking the kernel here are close to zero. An appropriate fix would be to replace that show_mem() call with something which can be safely called from all contexts in which the page allocator can be called.