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[209.132.180.67]) by mx.google.com with ESMTP id z7-v6si8987335pgz.284.2018.06.04.06.15.14; Mon, 04 Jun 2018 06:15:29 -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.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753150AbeFDNOr (ORCPT + 99 others); Mon, 4 Jun 2018 09:14:47 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:35939 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752839AbeFDNOp (ORCPT ); Mon, 4 Jun 2018 09:14:45 -0400 Received: from fsav305.sakura.ne.jp (fsav305.sakura.ne.jp [153.120.85.136]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id w54DDUX7019014; Mon, 4 Jun 2018 22:13:30 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav305.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav305.sakura.ne.jp); Mon, 04 Jun 2018 22:13:30 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav305.sakura.ne.jp) Received: from [192.168.1.8] (softbank126074194044.bbtec.net [126.74.194.44]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id w54DDPLa018979 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 4 Jun 2018 22:13:30 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: INFO: task hung in blk_queue_enter To: Dmitry Vyukov Cc: Bart Van Assche , LKML , linux-block@vger.kernel.org, Johannes Thumshirn , Alan Jenkins , syzbot , "Martin K. Petersen" , Jens Axboe , Dan Williams , Christoph Hellwig , oleksandr@natalenko.name, ming.lei@redhat.com, martin@lichtvoll.de, Hannes Reinecke , syzkaller-bugs , Ross Zwisler , keith.busch@intel.com, linux-ext4@vger.kernel.org References: <43327033306c3dd2f7c3717d64ce22415b6f3451.camel@wdc.com> <6db16aa3a7c56b6dcca2d10b4e100a780c740081.camel@wdc.com> <201805220652.BFH82351.SMQFFOJOtFOVLH@I-love.SAKURA.ne.jp> <201805222020.FEJ82897.OFtJMFHOVLQOSF@I-love.SAKURA.ne.jp> <25708e84-6f35-04c3-a2e4-6854f0ed9e78@I-love.SAKURA.ne.jp> From: Tetsuo Handa Message-ID: <09a33861-2ddc-1a13-19f6-2a1998ca3ec5@i-love.sakura.ne.jp> Date: Mon, 4 Jun 2018 22:13:23 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018/06/04 20:46, Dmitry Vyukov wrote: > On Fri, Jun 1, 2018 at 12:10 PM, Tetsuo Handa > wrote: >> Tetsuo Handa wrote: >>> Since sum of percpu_count did not change after percpu_ref_kill(), this is >>> not a race condition while folding percpu counter values into atomic counter >>> value. That is, for some reason, someone who is responsible for calling >>> percpu_ref_put(&q->q_usage_counter) (presumably via blk_queue_exit()) is >>> unable to call percpu_ref_put(). >>> But I don't know how to find someone who is failing to call percpu_ref_put()... >> >> I found the someone. It was already there in the backtrace... > > Nice! > > Do I understand it correctly that this bug is probably the root cause > of a whole lot of syzbot "task hung" reports? E.g. this one too? > https://syzkaller.appspot.com/bug?id=cdc4add60bb95a4da3fec27c5fe6d75196b7f976 > I guess we will need to sweep close everything related to > filesystems/block devices when this is committed? > I can't tell it. We still have lockdep warning for loop module. Also, I suspect that hung tasks waiting for page bit might be related to binder module. Since we are about to merge "kernel/hung_task.c: show all hung tasks before panic" patch, we might be able to get more hints after 4.18-rc1.