From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757546Ab3K0Sxx (ORCPT ); Wed, 27 Nov 2013 13:53:53 -0500 Received: from mail-yh0-f49.google.com ([209.85.213.49]:35151 "EHLO mail-yh0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753502Ab3K0Sxq (ORCPT ); Wed, 27 Nov 2013 13:53:46 -0500 Date: Wed, 27 Nov 2013 13:53:40 -0500 From: Tejun Heo To: Peter Zijlstra Cc: Li Zefan , John Stultz , Mel Gorman , Juri Lelli , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] cpuset: Fix memory allocator deadlock Message-ID: <20131127185340.GC13098@mtj.dyndns.org> References: <20131126140341.GL10022@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131126140341.GL10022@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 26, 2013 at 03:03:41PM +0100, Peter Zijlstra wrote: > Juri hit the below lockdep report: > > [ 4.303391] ====================================================== > [ 4.303392] [ INFO: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected ] > [ 4.303394] 3.12.0-dl-peterz+ #144 Not tainted > [ 4.303395] ------------------------------------------------------ > [ 4.303397] kworker/u4:3/689 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire: > [ 4.303399] (&p->mems_allowed_seq){+.+...}, at: [] new_slab+0x6c/0x290 > [ 4.303417] > [ 4.303417] and this task is already holding: > [ 4.303418] (&(&q->__queue_lock)->rlock){..-...}, at: [] blk_execute_rq_nowait+0x5b/0x100 > [ 4.303431] which would create a new lock dependency: > [ 4.303432] (&(&q->__queue_lock)->rlock){..-...} -> (&p->mems_allowed_seq){+.+...} > [ 4.303436] > > [ 4.303898] the dependencies between the lock to be acquired and SOFTIRQ-irq-unsafe lock: > [ 4.303918] -> (&p->mems_allowed_seq){+.+...} ops: 2762 { > [ 4.303922] HARDIRQ-ON-W at: > [ 4.303923] [] __lock_acquire+0x65a/0x1ff0 > [ 4.303926] [] lock_acquire+0x93/0x140 > [ 4.303929] [] kthreadd+0x86/0x180 > [ 4.303931] [] ret_from_fork+0x7c/0xb0 > [ 4.303933] SOFTIRQ-ON-W at: > [ 4.303933] [] __lock_acquire+0x68c/0x1ff0 > [ 4.303935] [] lock_acquire+0x93/0x140 > [ 4.303940] [] kthreadd+0x86/0x180 > [ 4.303955] [] ret_from_fork+0x7c/0xb0 > [ 4.303959] INITIAL USE at: > [ 4.303960] [] __lock_acquire+0x344/0x1ff0 > [ 4.303963] [] lock_acquire+0x93/0x140 > [ 4.303966] [] kthreadd+0x86/0x180 > [ 4.303969] [] ret_from_fork+0x7c/0xb0 > [ 4.303972] } > > Which reports that we take mems_allowed_seq with interrupts enabled. A > little digging found that this can only be from > cpuset_change_task_nodemask(). > > This is an actual deadlock because an interrupt doing an allocation will > hit get_mems_allowed()->...->__read_seqcount_begin(), which will spin > forever waiting for the write side to complete. > > Cc: John Stultz > Cc: Mel Gorman > Reported-by: Juri Lelli > Signed-off-by: Peter Zijlstra Applied to cgroup/for-3.13-fixes w/ stable cc'd. Thanks. -- tejun