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 0C37DC43381 for ; Tue, 19 Mar 2019 04:28:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CCB4D2085A for ; Tue, 19 Mar 2019 04:28:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725290AbfCSE2P (ORCPT ); Tue, 19 Mar 2019 00:28:15 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60132 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725287AbfCSE2P (ORCPT ); Tue, 19 Mar 2019 00:28:15 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id DEB593082B07; Tue, 19 Mar 2019 04:28:14 +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 748F219C67; Tue, 19 Mar 2019 04:28:09 +0000 (UTC) Date: Tue, 19 Mar 2019 12:28:04 +0800 From: Ming Lei To: James Smart Cc: 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: <20190319042803.GD22459@ming.t460p> References: <20190318032950.17770-1-ming.lei@redhat.com> <20190318032950.17770-2-ming.lei@redhat.com> <4563485a-02c6-0bfe-d9ec-49adbd44671c@broadcom.com> <20190319013142.GB22459@ming.t460p> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.1 (2017-09-22) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Tue, 19 Mar 2019 04:28:14 +0000 (UTC) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Mon, Mar 18, 2019 at 09:04:37PM -0700, James Smart wrote: > > > On 3/18/2019 6:31 PM, Ming Lei wrote: > > On Mon, Mar 18, 2019 at 10:37:08AM -0700, James Smart wrote: > > > > > > On 3/17/2019 8:29 PM, Ming Lei wrote: > > > > In NVMe's error handler, follows the typical steps for tearing down > > > > hardware: > > > > > > > > 1) stop blk_mq hw queues > > > > 2) stop the real hw queues > > > > 3) cancel in-flight requests via > > > > blk_mq_tagset_busy_iter(tags, cancel_request, ...) > > > > cancel_request(): > > > > mark the request as abort > > > > blk_mq_complete_request(req); > > > > 4) destroy real hw queues > > > > > > > > However, there may be race between #3 and #4, because blk_mq_complete_request() > > > > actually completes the request asynchronously. > > > > > > > > This patch introduces blk_mq_complete_request_sync() for fixing the > > > > above race. > > > > > > > This won't help FC at all. Inherently, the "completion" has to be > > > asynchronous as line traffic may be required. > > > > > > e.g. FC doesn't use nvme_complete_request() in the iterator routine. > > > > > Looks FC has done the sync already, see nvme_fc_delete_association(): > > > > ... > > /* wait for all io that had to be aborted */ > > spin_lock_irq(&ctrl->lock); > > wait_event_lock_irq(ctrl->ioabort_wait, ctrl->iocnt == 0, ctrl->lock); > > ctrl->flags &= ~FCCTRL_TERMIO; > > spin_unlock_irq(&ctrl->lock); > > yes - but the iterator started a lot of the back end io terminating in > parallel. So waiting on many happening in parallel is better than waiting 1 > at a time. OK, that is FC's sync, not related with this patch. > Even so, I've always disliked this wait and would have > preferred to exit the thread with something monitoring the completions > re-queuing a work thread to finish. Then I guess you may like this patch given it actually avoids the potential wait, :-) What the patch does is to convert the remote completion(#1) into local completion(#2): 1) previously one request may be completed remotely by blk_mq_complete_request(): rq->csd.func = __blk_mq_complete_request_remote; rq->csd.info = rq; rq->csd.flags = 0; smp_call_function_single_async(ctx->cpu, &rq->csd); 2) this patch changes the remote completion into local completion via blk_mq_complete_request_sync(), so all in-flight requests can be aborted before destroying queue. q->mq_ops->complete(rq); As I mentioned in another email, there isn't any waiting for aborting request, nvme_cancel_request() simply requeues the request to blk-mq under this situation. Thanks, Ming