From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f178.google.com ([209.85.220.178]:39525 "EHLO mail-qk0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752795AbeAHR11 (ORCPT ); Mon, 8 Jan 2018 12:27:27 -0500 Date: Mon, 8 Jan 2018 09:27:23 -0800 From: Tejun Heo To: "jianchao.wang" Cc: jbacik@fb.com, jack@suse.cz, axboe@kernel.dk, clm@fb.com, kernel-team@fb.com, linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org, peterz@infradead.org, Bart.VanAssche@wdc.com Subject: Re: [PATCH 5/7] blk-mq: remove REQ_ATOM_COMPLETE usages from blk-mq Message-ID: <20180108172723.GY3668920@devbig577.frc2.facebook.com> References: <20171216120726.517153-1-tj@kernel.org> <20171216120726.517153-6-tj@kernel.org> <64dfa760-d433-1537-9bc6-b12cda3c9dc6@oracle.com> <20171221135051.GE1084507@devbig577.frc2.facebook.com> <4e5aa629-f341-d077-961b-c778ceb31154@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <4e5aa629-f341-d077-961b-c778ceb31154@oracle.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: Hello, Jianchao. On Fri, Dec 22, 2017 at 12:02:20PM +0800, jianchao.wang wrote: > > On Thu, Dec 21, 2017 at 11:56:49AM +0800, jianchao.wang wrote: > >> It's worrying that even though the blk_mark_rq_complete() here is > >> intended to synchronize with timeout path, but it indeed give the > >> blk_mq_complete_request() the capability to exclude with > > There could be scenario where the driver itself stop a request > itself with blk_mq_complete_request() or some other interface that > will invoke it, races with the normal completion path where a same > request comes. But what'd prevent the completion reinitializing the request and then the actual completion path coming in and completing the request again? > For example: > a reset could be triggered through sysfs on nvme-rdma > Then the driver will cancel all the reqs, including in-flight ones. > nvme_rdma_reset_ctrl_work() > nvme_rdma_shutdown_ctrl() > >>>> > if (ctrl->ctrl.queue_count > 1) { > nvme_stop_queues(&ctrl->ctrl); //quiesce the queue > blk_mq_tagset_busy_iter(&ctrl->tag_set, > nvme_cancel_request, &ctrl->ctrl); //invoke blk_mq_complete_request() > nvme_rdma_destroy_io_queues(ctrl, shutdown); > } > >>>> > > These operations could race with the normal completion path of in-flight ones. > It should drain all the in-flight ones first here. But there maybe some other > places similar with this. If there are any such places, they should be using an interface which is propelry synchronized like blk_abort_request(), which btw is what libata already does. Otherwise, it's racy with or without these patches. Thanks. -- tejun