Delivered-To: jwboyer@gmail.com Received: by 10.76.168.104 with SMTP id zv8csp55663oab; Fri, 30 Aug 2013 15:52:46 -0700 (PDT) X-Received: by 10.68.244.168 with SMTP id xh8mr12419215pbc.3.1377903166373; Fri, 30 Aug 2013 15:52:46 -0700 (PDT) Return-Path: Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67]) by mx.google.com with ESMTP id qc9si280431pac.269.1969.12.31.16.00.00; Fri, 30 Aug 2013 15:52:46 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mail=linux-kernel-owner@vger.kernel.org; dkim=neutral (bad format) header.i=@hds.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753535Ab3H3WrV (ORCPT + 99 others); Fri, 30 Aug 2013 18:47:21 -0400 Received: from usindpps04.hds.com ([207.126.252.17]:35636 "EHLO usindpps04.hds.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752650Ab3H3WrU (ORCPT ); Fri, 30 Aug 2013 18:47:20 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=hds.com; h=subject : to : from : cc : date : message-id : mime-version : content-type : content-transfer-encoding; s=mail1; bh=VofHN8IMnygn2hbqnFjLmX0PPEPbvpzE377u1RxpGOY=; b=piW6J78W57qDXBPJJuodWw/tvf0T//JbxKX6sLPvpuaOG2nBLMHzDqUeTYwFEQqUvdmf ZTkiwsKi0WEku3MKcxJ7veR7wvTZcQ4fGMETFTf1c2J/1JOKpXLnft4ERuW89/FAxw25 wQM1ulsuQ3Cncl0I/sIaqMlaMOtvuQ/C8rsHorp+75eFiL6yx1jU5wMbuti4D/NprIET 3r57cPZ0YCh6sLjvOgjay6mKyktMToyjHPx6X1TWCSWcwes33Popc1hpadxUdFI/0npL mN3Tttbe7e2RcmkXAZbwg8xj+FwSu3nIRC4G9UpFCsMz518C/AWZj4puwWE6VHZWVvVZ Rg== Received: from usindmail01.hds.com (usindmail03 [207.126.252.22]) by usindpps04.hds.com (8.14.5/8.14.5) with ESMTP id r7UMlBjr025492; Fri, 30 Aug 2013 18:47:11 -0400 Received: from hds.com (usindnetf5d-vlan47float.corp.hds.com [10.74.73.11]) by usindmail01.hds.com (8.14.1/8.14.1) with ESMTP id r7UMl8SG058466; Fri, 30 Aug 2013 18:47:10 -0400 (EDT) Subject: [PATCH v2 1/2] elevator: Fix a race in elevator switching and md device initialization To: linux-kernel@vger.kernel.org From: Tomoki Sekiyama Cc: axboe@kernel.dk, tj@kernel.org, seiji.aguchi@hds.com, vgoyal@redhat.com, majianpeng@gmail.com Date: Fri, 30 Aug 2013 18:47:07 -0400 Message-ID: <20130830224707.21812.63516.stgit@hds.com> User-Agent: StGit/0.16 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Proofpoint-SPF-Result: pass X-Proofpoint-SPF-Record: v=spf1 mx ip4:207.126.244.0/26 ip4:207.126.252.0/25 include:mktomail.com include:cloud.hds.com ~all X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:5.10.8794,1.0.431,0.0.0000 definitions=2013-08-30_09:2013-08-30,2013-08-30,1970-01-01 signatures=0 X-Proofpoint-Spam-Details: rule=notspam policy=outbound_policy score=0 spamscore=0 suspectscore=1 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=7.0.1-1305240000 definitions=main-1308300162 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The soft lockup below happens at the boot time of the system using dm multipath and the udev rules to switch scheduler. [ 356.127001] BUG: soft lockup - CPU#3 stuck for 22s! [sh:483] [ 356.127001] RIP: 0010:[] [] lock_timer_base.isra.35+0x1d/0x50 ... [ 356.127001] Call Trace: [ 356.127001] [] try_to_del_timer_sync+0x20/0x70 [ 356.127001] [] ? kmem_cache_alloc_node_trace+0x20a/0x230 [ 356.127001] [] del_timer_sync+0x52/0x60 [ 356.127001] [] cfq_exit_queue+0x32/0xf0 [ 356.127001] [] elevator_exit+0x2f/0x50 [ 356.127001] [] elevator_change+0xf1/0x1c0 [ 356.127001] [] elv_iosched_store+0x20/0x50 [ 356.127001] [] queue_attr_store+0x59/0xb0 [ 356.127001] [] sysfs_write_file+0xc6/0x140 [ 356.127001] [] vfs_write+0xbd/0x1e0 [ 356.127001] [] SyS_write+0x49/0xa0 [ 356.127001] [] system_call_fastpath+0x16/0x1b This is caused by a race between md device initialization by multipathd and shell script to switch the scheduler using sysfs. - multipathd: SyS_ioctl -> do_vfs_ioctl -> dm_ctl_ioctl -> ctl_ioctl -> table_load -> dm_setup_md_queue -> blk_init_allocated_queue -> elevator_init q->elevator = elevator_alloc(q, e); // not yet initialized - sh -c 'echo deadline > /sys/$DEVPATH/queue/scheduler': elevator_switch (in the call trace above) struct elevator_queue *old = q->elevator; q->elevator = elevator_alloc(q, new_e); elevator_exit(old); // lockup! (*) - multipathd: (cont.) err = e->ops.elevator_init_fn(q); // init fails; q->elevator is modified (*) When del_timer_sync() is called, lock_timer_base() will loop infinitely while timer->base == NULL. In this case, as timer will never initialized, it results in lockup. This patch introduces acquisition of q->sysfs_lock around elevator_init() into blk_init_allocated_queue(), to provide mutual exclusion between initialization of the q->scheduler and switching of the scheduler. This should fix this bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=902012 Signed-off-by: Tomoki Sekiyama --- block/blk-core.c | 10 +++++++++- block/elevator.c | 6 ++++++ 2 files changed, 15 insertions(+), 1 deletion(-) diff --git a/block/blk-core.c b/block/blk-core.c index 93a18d1..2f6275f 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -739,9 +739,17 @@ blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn, q->sg_reserved_size = INT_MAX; + /* Protect q->elevator from elevator_change */ + mutex_lock(&q->sysfs_lock); + /* init elevator */ - if (elevator_init(q, NULL)) + if (elevator_init(q, NULL)) { + mutex_unlock(&q->sysfs_lock); return NULL; + } + + mutex_unlock(&q->sysfs_lock); + return q; } EXPORT_SYMBOL(blk_init_allocated_queue); diff --git a/block/elevator.c b/block/elevator.c index 668394d..02d4390 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -186,6 +186,12 @@ int elevator_init(struct request_queue *q, char *name) struct elevator_type *e = NULL; int err; + /* + * q->sysfs_lock must be held to provide mutual exclusion between + * elevator_switch() and here. + */ + lockdep_assert_held(&q->sysfs_lock); + if (unlikely(q->elevator)) return 0; -- 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/