Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932147Ab1BRStR (ORCPT ); Fri, 18 Feb 2011 13:49:17 -0500 Received: from smtp1.linux-foundation.org ([140.211.169.13]:48713 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756314Ab1BRStO convert rfc822-to-8bit (ORCPT ); Fri, 18 Feb 2011 13:49:14 -0500 MIME-Version: 1.0 In-Reply-To: References: <20110216185234.GA11636@tiehlicka.suse.cz> <20110216193700.GA6377@elte.hu> <20110217090910.GA3781@tiehlicka.suse.cz> <20110217163531.GF14168@elte.hu>

<20110218122938.GB26779@tiehlicka.suse.cz> <20110218162623.GD4862@tiehlicka.suse.cz> From: Linus Torvalds Date: Fri, 18 Feb 2011 10:48:18 -0800 Message-ID: Subject: Re: BUG: Bad page map in process udevd (anon_vma: (null)) in 2.6.38-rc4 To: "Eric W. Biederman" Cc: Michal Hocko , Ingo Molnar , linux-mm@kvack.org, LKML , David Miller , Eric Dumazet , netdev@vger.kernel.org, Arnaldo Carvalho de Melo Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3122 Lines: 76 On Fri, Feb 18, 2011 at 10:08 AM, Eric W. Biederman wrote: > > I am still getting programs segfaulting but that is happening on other > machines running on older kernels so I am going to chalk that up to a > buggy test and a false positive. Ok. > I am have OOM problems getting my tests run to complete. ?On a good > day that happens about 1 time in 3 right now. ?I'm guess I will have > to turn off DEBUG_PAGEALLOC to get everything to complete. > DEBUG_PAGEALLOC causes us to use more memory doesn't it? It does use a bit more memory, but it shouldn't be _that_ noticeable. The real cost of DEBUG_PAGEALLOC is all the crazy page table operations and TLB flushes we do for each allocation/deallocation. So DEBUG_PAGEALLOC is very CPU-intensive, but it shouldn't have _that_ much of a memory overhead - just some trivial overhead due to not being able to use largepages for the normal kernel identity mappings. But there might be some other interaction with OOM that I haven't thought about. > The most interesting thing I have right now is a networking lockdep > issue. ?Does anyone know what is going on there? This seems to be a fairly straightforward bug. In net/ipv4/inet_timewait_sock.c we have this: /* These are always called from BH context. See callers in * tcp_input.c to verify this. */ /* This is for handling early-kills of TIME_WAIT sockets. */ void inet_twsk_deschedule(struct inet_timewait_sock *tw, struct inet_timewait_death_row *twdr) { spin_lock(&twdr->death_lock); .. and the intention is clearly that that spin_lock is BH-safe because it's called from BH context. Except that clearly isn't true. It's called from a worker thread: > stack backtrace: > Pid: 10833, comm: kworker/u:1 Not tainted 2.6.38-rc4-359399.2010AroraKernelBeta.fc14.x86_64 #1 > Call Trace: > ?[] ? inet_twsk_deschedule+0x29/0xa0 > ?[] ? inet_twsk_purge+0xf6/0x180 > ?[] ? inet_twsk_purge+0x30/0x180 > ?[] ? tcp_sk_exit_batch+0x1c/0x20 > ?[] ? ops_exit_list.clone.0+0x53/0x60 > ?[] ? cleanup_net+0x100/0x1b0 > ?[] ? process_one_work+0x187/0x4b0 > ?[] ? process_one_work+0x121/0x4b0 > ?[] ? cleanup_net+0x0/0x1b0 > ?[] ? worker_thread+0x15c/0x330 so it can deadlock with a BH happening at the same time, afaik. The code (and comment) is all from 2005, it looks like the BH->worker thread has broken the code. But somebody who knows that code better should take a deeper look at it. Added acme to the cc, since the code is attributed to him back in 2005 ;). Although I don't know how active he's been in networking lately (seems to be all perf-related). Whatever, it can't hurt. Linus -- 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/