From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: [bdi_unregister] 165a5e22fa INFO: task swapper:1 blocked for more than 120 seconds. Date: Mon, 06 Mar 2017 06:35:21 -0800 Message-ID: <1488810921.16832.6.camel@linux.vnet.ibm.com> References: <20170305022111.yqtwyd6ognmco4gx@wfg-t540p.sh.intel.com> <20170306102733.GC14932@quack2.suse.cz> <20170306120123.GD14932@quack2.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:37908 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932456AbdCFOfg (ORCPT ); Mon, 6 Mar 2017 09:35:36 -0500 Received: from pps.filterd (m0098394.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v26ETDxU144581 for ; Mon, 6 Mar 2017 09:35:30 -0500 Received: from e19.ny.us.ibm.com (e19.ny.us.ibm.com [129.33.205.209]) by mx0a-001b2d01.pphosted.com with ESMTP id 2918g6bkwb-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 06 Mar 2017 09:35:29 -0500 Received: from localhost by e19.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 6 Mar 2017 09:35:28 -0500 In-Reply-To: <20170306120123.GD14932@quack2.suse.cz> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Jan Kara , Fengguang Wu Cc: Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, LKP , "Martin K. Petersen" , linux-scsi@vger.kernel.org On Mon, 2017-03-06 at 13:01 +0100, Jan Kara wrote: > On Mon 06-03-17 11:27:33, Jan Kara wrote: > > Hi, > > > > On Sun 05-03-17 10:21:11, Wu Fengguang wrote: > > > FYI next-20170303 is good while mainline is bad with this error. > > > The attached reproduce-* may help reproduce the issue. > > > > Thanks for report! So from the stacktrace we are in the path > > testing removal of a device immediately after it has been probed > > and for some reason bdi_unregister() hangs - likely waiting for > > cgroup-writeback references to drop. Given how early this happens > > my guess is we fail to initialize something but for now I don't see > > how my patch could make a difference. I'm trying to reproduce this > > to be able to debug more... > > OK, so after some debugging I think this is yet another problem in > SCSI initialization / destruction code which my patch only makes > visible (added relevant maintainers). > > I can reproduce the problem reliably with enabling: > > CONFIG_DEBUG_TEST_DRIVER_REMOVE=y > CONFIG_SCSI_DEBUG=m > CONFIG_BLK_CGROUP=y > CONFIG_MEMCG=y > (and thus CONFIG_CGROUP_WRITEBACK=y) > > then 'modprobe scsi_debug' is all it takes to reproduce hang. > Relevant kernel messages with some of my debugging added (attached is > a patch that adds those debug messages): This looks to be precisely the same problem Dan Williams was debugging for us. > [ 58.721765] scsi host0: scsi_debug: version 1.86 [20160430] > [ 58.721765] dev_size_mb=8, opts=0x0, submit_queues=1, > statistics=0 > [ 58.728946] CGWB init ffff88007fbb2000 > [ 58.730095] Created sdev ffff880078e1a000 > [ 58.731611] scsi 0:0:0:0: Direct-Access Linux scsi_debug > 0186 PQ : 0 ANSI: 7 > [ 58.782246] sd 0:0:0:0: [sda] 16384 512-byte logical blocks: (8.39 > MB/8.00 MiB) > [ 58.789687] sd 0:0:0:0: [sda] Write Protect is off > [ 58.791140] sd 0:0:0:0: [sda] Mode Sense: 73 00 10 08 > [ 58.800879] sd 0:0:0:0: [sda] Write cache: enabled, read cache: > enabled, supports DPO and FUA > [ 58.893738] sd 0:0:0:0: [sda] Attached SCSI disk > [ 58.896808] Unreg1 > [ 58.897960] Unreg2 > [ 58.898637] Unreg3 > [ 58.899100] CGWB ffff88007fbb2000 usage_cnt: 0 > [ 58.900004] Unreg4 > [ 58.904976] sd 0:0:0:0: [sda] Synchronizing SCSI cache OK, can you put a WARN_ON trace in sd_shutdown and tell us where this is coming from. For the device to be reused after this we have to be calling sd_shutdown() without going into SDEV_DEL. Thanks, James