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 X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0EC17C43381 for ; Thu, 21 Mar 2019 01:39:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D3D76218C3 for ; Thu, 21 Mar 2019 01:39:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726753AbfCUBjU (ORCPT ); Wed, 20 Mar 2019 21:39:20 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39164 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726487AbfCUBjT (ORCPT ); Wed, 20 Mar 2019 21:39:19 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 84FE930832CD; Thu, 21 Mar 2019 01:39:19 +0000 (UTC) Received: from ming.t460p (ovpn-8-18.pek2.redhat.com [10.72.8.18]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2110D600C1; Thu, 21 Mar 2019 01:39:13 +0000 (UTC) Date: Thu, 21 Mar 2019 09:39:09 +0800 From: Ming Lei To: Sagi Grimberg Cc: Bart Van Assche , Jens Axboe , linux-block@vger.kernel.org, Christoph Hellwig , linux-nvme@lists.infradead.org Subject: Re: [PATCH 1/2] blk-mq: introduce blk_mq_complete_request_sync() Message-ID: <20190321013908.GA15115@ming.t460p> References: <20190318032950.17770-1-ming.lei@redhat.com> <20190318032950.17770-2-ming.lei@redhat.com> <20190318073826.GA29746@ming.t460p> <1552921495.152266.8.camel@acm.org> <20190318151618.GA20371@ming.t460p> <1552924164.152266.21.camel@acm.org> <448615db-64e2-cbe7-c09e-19b2d86a720a@grimberg.me> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <448615db-64e2-cbe7-c09e-19b2d86a720a@grimberg.me> User-Agent: Mutt/1.9.1 (2017-09-22) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Thu, 21 Mar 2019 01:39:19 +0000 (UTC) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Wed, Mar 20, 2019 at 05:47:01PM -0700, Sagi Grimberg wrote: > > > Hi Ming, > > > > Just like the NVMeOF initiator driver, the SRP initiator driver uses an > > RDMA RC connection for all of its communication over the network. If > > communication between initiator and target fails the target driver will > > close the connection or one of the work requests that was posted by the > > initiator driver will complete with an error status (wc->status != > > IB_WC_SUCCESS). In the latter case the function srp_handle_qp_err() will > > try to reestablish the connection between initiator and target after a > > certain delay: > > > > if (delay > 0) > > queue_delayed_work(system_long_wq, &rport->reconnect_work, > > 1UL * delay * HZ); > > > > SCSI timeouts may kick the SCSI error handler. That results in calls of > > the srp_reset_device() and/or srp_reset_host() functions. srp_reset_host() > > terminates all outstanding requests after having disconnected the RDMA RC > > connection. Disconnecting the RC connection first guarantees that there > > are no concurrent request completion calls from the regular completion > > path and from the error handler. > > Hi Bart, > > If I understand the race correctly, its not between the requests > completion and the queue pairs removal nor the timeout handler > necessarily, but rather it is between the async requests completion and > the tagset deallocation. > > Think of surprise removal (or disconnect) during I/O, drivers > usually stop/quiesce/freeze the queues, terminate/abort inflight > I/Os and then teardown the hw queues and the tagset. > > IIRC, the same race holds for srp if this happens during I/O: > 1. srp_rport_delete() -> srp_remove_target() -> srp_stop_rport_timers() -> > __rport_fail_io_fast() > > 2. complete all I/Os (async remotely via smp) > > Then continue.. > > 3. scsi_host_put() -> scsi_host_dev_release() -> scsi_mq_destroy_tags() > > What is preventing (3) from happening before (2) if its async? I would > think that scsi drivers need the exact same thing... blk_cleanup_queue() will do that, but it can't be used in device recovery obviously. BTW, blk_mq_complete_request_sync() is a bit misleading, maybe blk_mq_complete_request_locally() is better. Thanks, Ming