From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755407AbdEDN5U (ORCPT ); Thu, 4 May 2017 09:57:20 -0400 Received: from mail-io0-f180.google.com ([209.85.223.180]:33199 "EHLO mail-io0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755408AbdEDN5A (ORCPT ); Thu, 4 May 2017 09:57:00 -0400 Subject: Re: [PATCH] block/mq: Cure cpu hotplug lock inversion To: Peter Zijlstra , Thomas Gleixner , Sebastian Andrzej Siewior References: <20170504130526.wvpagnb7f4lw2ih4@hirez.programming.kicks-ass.net> Cc: linux-kernel@vger.kernel.org From: Jens Axboe Message-ID: <46063288-15e3-a788-b6f0-8d1397f02fbe@kernel.dk> Date: Thu, 4 May 2017 07:56:57 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <20170504130526.wvpagnb7f4lw2ih4@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/04/2017 07:05 AM, Peter Zijlstra wrote: > > By poking at /debug/sched_features I triggered the following splat: > > [] ====================================================== > [] WARNING: possible circular locking dependency detected > [] 4.11.0-00873-g964c8b7-dirty #694 Not tainted > [] ------------------------------------------------------ > [] bash/2109 is trying to acquire lock: > [] (cpu_hotplug_lock.rw_sem){++++++}, at: [] static_key_slow_dec+0x1b/0x50 > [] > [] but task is already holding lock: > [] (&sb->s_type->i_mutex_key#4){+++++.}, at: [] sched_feat_write+0x86/0x170 > [] > [] which lock already depends on the new lock. > [] > [] > [] the existing dependency chain (in reverse order) is: > [] > [] -> #2 (&sb->s_type->i_mutex_key#4){+++++.}: > [] lock_acquire+0x100/0x210 > [] down_write+0x28/0x60 > [] start_creating+0x5e/0xf0 > [] debugfs_create_dir+0x13/0x110 > [] blk_mq_debugfs_register+0x21/0x70 > [] blk_mq_register_dev+0x64/0xd0 > [] blk_register_queue+0x6a/0x170 > [] device_add_disk+0x22d/0x440 > [] loop_add+0x1f3/0x280 > [] loop_init+0x104/0x142 > [] do_one_initcall+0x43/0x180 > [] kernel_init_freeable+0x1de/0x266 > [] kernel_init+0xe/0x100 > [] ret_from_fork+0x31/0x40 > [] > [] -> #1 (all_q_mutex){+.+.+.}: > [] lock_acquire+0x100/0x210 > [] __mutex_lock+0x6c/0x960 > [] mutex_lock_nested+0x1b/0x20 > [] blk_mq_init_allocated_queue+0x37c/0x4e0 > [] blk_mq_init_queue+0x3a/0x60 > [] loop_add+0xe5/0x280 > [] loop_init+0x104/0x142 > [] do_one_initcall+0x43/0x180 > [] kernel_init_freeable+0x1de/0x266 > [] kernel_init+0xe/0x100 > [] ret_from_fork+0x31/0x40 > > [] *** DEADLOCK *** > [] > [] 3 locks held by bash/2109: > [] #0: (sb_writers#11){.+.+.+}, at: [] vfs_write+0x17d/0x1a0 > [] #1: (debugfs_srcu){......}, at: [] full_proxy_write+0x5d/0xd0 > [] #2: (&sb->s_type->i_mutex_key#4){+++++.}, at: [] sched_feat_write+0x86/0x170 > [] > [] stack backtrace: > [] CPU: 9 PID: 2109 Comm: bash Not tainted 4.11.0-00873-g964c8b7-dirty #694 > [] Hardware name: Intel Corporation S2600GZ/S2600GZ, BIOS SE5C600.86B.02.02.0002.122320131210 12/23/2013 > [] Call Trace: > > [] lock_acquire+0x100/0x210 > [] get_online_cpus+0x2a/0x90 > [] static_key_slow_dec+0x1b/0x50 > [] static_key_disable+0x20/0x30 > [] sched_feat_write+0x131/0x170 > [] full_proxy_write+0x97/0xd0 > [] __vfs_write+0x28/0x120 > [] vfs_write+0xb5/0x1a0 > [] SyS_write+0x49/0xa0 > [] entry_SYSCALL_64_fastpath+0x23/0xc2 > > This is because of the cpu hotplug lock rework. Break the chain at #1 > by reversing the lock acquisition order. This way i_mutex_key#4 no > longer depends on cpu_hotplug_lock and things are good. Thanks Peter, applied. -- Jens Axboe