From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1FFA2C433EF for ; Mon, 14 Feb 2022 01:08:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232401AbiBNBI2 (ORCPT ); Sun, 13 Feb 2022 20:08:28 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:33604 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231489AbiBNBI1 (ORCPT ); Sun, 13 Feb 2022 20:08:27 -0500 Received: from www262.sakura.ne.jp (www262.sakura.ne.jp [202.181.97.72]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1B973527D0; Sun, 13 Feb 2022 17:08:20 -0800 (PST) Received: from fsav314.sakura.ne.jp (fsav314.sakura.ne.jp [153.120.85.145]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 21E183vd050563; Mon, 14 Feb 2022 10:08:03 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav314.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav314.sakura.ne.jp); Mon, 14 Feb 2022 10:08:03 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav314.sakura.ne.jp) Received: from [192.168.1.9] (M106072142033.v4.enabler.ne.jp [106.72.142.33]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 21E1825Z050560 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NO); Mon, 14 Feb 2022 10:08:03 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Message-ID: <2959649d-cfbc-bdf2-02ac-053b8e7af030@I-love.SAKURA.ne.jp> Date: Mon, 14 Feb 2022 10:08:00 +0900 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.6.0 Subject: Re: [syzbot] possible deadlock in worker_thread Content-Language: en-US To: Bart Van Assche , syzbot , jgg@ziepe.ca, linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org, syzkaller-bugs@googlegroups.com, Tejun Heo , Lai Jiangshan References: <0000000000005975a605d7aef05e@google.com> <8ea57ddf-a09c-43f2-4285-4dfb908ad967@acm.org> <71d6f14e-46af-cc5a-bc70-af1cdc6de8d5@acm.org> <309c86b7-2a4c-1332-585f-7bcd59cfd762@I-love.SAKURA.ne.jp> From: Tetsuo Handa In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On 2022/02/14 8:06, Bart Van Assche wrote: > On 2/12/22 09:14, Tetsuo Handa wrote: >> How can reviewing all flush_workqueue(system_long_wq) calls help? > > It is allowed to queue blocking actions on system_long_wq. Correct. > flush_workqueue(system_long_wq) can make a lower layer (e.g. ib_srp) > wait on a blocking action from a higher layer (e.g. the loop driver) > and thereby cause a deadlock. Correct. > Hence my proposal to review all flush_workqueue(system_long_wq) calls. Maybe I'm misunderstanding what the "review" means. My proposal is to "rewrite" any module which needs to call flush_workqueue() on system-wide workqueues or call flush_work()/flush_*_work() which will depend on system-wide workqueues. That is, for example, "rewrite" ib_srp module not to call flush_workqueue(system_long_wq). + srp_tl_err_wq = alloc_workqueue("srp_tl_err_wq", 0, 0); - queue_work(system_long_wq, &target->tl_err_work); + queue_work(srp_tl_err_wq, &target->tl_err_work); - flush_workqueue(system_long_wq); + flush_workqueue(srp_tl_err_wq); + destroy_workqueue(srp_tl_err_wq); Then, we can call WARN_ON() if e.g. flush_workqueue() is called on system-wide workqueues.