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=-2.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=unavailable 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 DF3D0C10F05 for ; Wed, 27 Mar 2019 02:14:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B3F37206B7 for ; Wed, 27 Mar 2019 02:14:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553652855; bh=VvHZ5vGJk7HrBd2fmAGJZqonihBIEkH9NHMMoNjL9Yw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=BzkEiiFQDgwMTjUQ7LV1vdGH3NKzLotHDYHJkKRSET2oB8HqrJ5jU0IuovYcHmFGM KsH0ZXNUEQm+EepacrAun+16ooPG0FdUoYeb6LbhB6SukgDM8FlneAD1ri2NkQJt5r Ay14jh6h0FYGWLQm6O3ruu9E6lcYit/oH0TrK/pI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732097AbfC0COO (ORCPT ); Tue, 26 Mar 2019 22:14:14 -0400 Received: from mga01.intel.com ([192.55.52.88]:2329 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726922AbfC0COO (ORCPT ); Tue, 26 Mar 2019 22:14:14 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by fmsmga101.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 26 Mar 2019 19:14:13 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.60,274,1549958400"; d="scan'208";a="130476793" Received: from unknown (HELO localhost.localdomain) ([10.232.112.69]) by orsmga006.jf.intel.com with ESMTP; 26 Mar 2019 19:14:11 -0700 Date: Tue, 26 Mar 2019 20:15:22 -0600 From: Keith Busch To: "jianchao.wang" Cc: Jens Axboe , linux-block , James Smart , Bart Van Assche , Ming Lei , Josef Bacik , linux-nvme , Linux Kernel Mailing List , "Busch, Keith" , Hannes Reinecke , Johannes Thumshirn , Christoph Hellwig , Sagi Grimberg Subject: Re: [PATCH V2 7/8] nvme: use blk_mq_queue_tag_inflight_iter Message-ID: <20190327021521.GA7389@localhost.localdomain> References: <1553492318-1810-1-git-send-email-jianchao.w.wang@oracle.com> <1553492318-1810-8-git-send-email-jianchao.w.wang@oracle.com> <20190325134917.GA4328@localhost.localdomain> <70e14e12-2ffc-37db-dd8f-229bc580546e@oracle.com> <20190326235726.GC4328@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 27, 2019 at 10:03:26AM +0800, jianchao.wang wrote: > Hi Keith > > On 3/27/19 7:57 AM, Keith Busch wrote: > > On Mon, Mar 25, 2019 at 08:05:53PM -0700, jianchao.wang wrote: > >> What if there used to be a io scheduler and leave some stale requests of sched tags ? > >> Or the nr_hw_queues was decreased and leave the hctx->fq->flush_rq ? > > > > Requests internally queued in scheduler or block layer are not eligible > > for the nvme driver's iterator callback. We only use it to reclaim > > dispatched requests that the target can't return, which only applies to > > requests that must have a valid rq->tag value from hctx->tags. > > > >> The stable request could be some tings freed and used > >> by others and the state field happen to be overwritten to non-zero... > > > > I am not sure I follow what this means. At least for nvme, every queue > > sharing the same tagset is quiesced and frozen, there should be no > > request state in flux at the time we iterate. > > > > In nvme_dev_disable, when we try to reclaim the in-flight requests with blk_mq_tagset_busy_iter, > the request_queues are quiesced but just start-freeze. > We will try to _drain_ the in-flight requests for the _shutdown_ case when controller is not dead. > For the reset case, there still could be someone escapes the checking of queue freezing and enters > blk_mq_make_request and tries to allocate tag, then we may get, > > generic_make_request nvme_dev_disable > -> blk_queue_enter > -> nvme_start_freeze (just start freeze, no drain) > -> nvme_stop_queues > -> blk_mq_make_request > - > blk_mq_get_request -> blk_mq_tagset_busy_iter > -> blk_mq_get_tag > 　　 -> bt_tags_for_each > 　　　 -> bt_tags_iter > 　　 -> rq = tags->rqs[] ---> [1] > -> blk_mq_rq_ctx_init > -> data->hctx->tags->rqs[rq->tag] = rq; > > The rq got on position [1] could be a stale request that has been freed due to, > 1. a hctx->fq.flush_rq of dead request_queue that shares the same tagset > 2. a removed io scheduler's sched request > > And this stale request may have been used by others and the request->state is changed to a non-zero > value and passes the checking of blk_mq_request_started and then it will be handled by nvme_cancel_request. How is that request state going to be anyting other than IDLE? A freed request state is IDLE, and continues to be IDLE until dispatched. But dispatch is blocked for the entire tagset, so request states can't be started during an nvme reset.