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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D763FC433EF for ; Wed, 29 Sep 2021 15:28:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AD78C61462 for ; Wed, 29 Sep 2021 15:28:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345237AbhI2P35 (ORCPT ); Wed, 29 Sep 2021 11:29:57 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:53213 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345201AbhI2P35 (ORCPT ); Wed, 29 Sep 2021 11:29:57 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1632929296; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=T93jqqgqqFV2Mt29ptOHTmBc09wsel2Yq+k09RyZmL4=; b=YJKwwCnpKEF9MehkKDqGZbHShcMB0BrxnSXtAAynm/MgrR7cRiVNq7NQ6aK20Y+cS5E7/v AjNTZGrHxIVed6FRWGFizgNwBbnBKaTGscyptDA6qzbmkX29j0ahWwOJncq2rynd+BLuh2 gubm/k4FdlfCYpTiPY9WgrH/VHyUV3w= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-126-mEyAJEfYOHOC89svWV9gJA-1; Wed, 29 Sep 2021 11:28:12 -0400 X-MC-Unique: mEyAJEfYOHOC89svWV9gJA-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4553336301; Wed, 29 Sep 2021 15:28:11 +0000 (UTC) Received: from T590 (ovpn-8-25.pek2.redhat.com [10.72.8.25]) by smtp.corp.redhat.com (Postfix) with ESMTPS id DE6DF19C59; Wed, 29 Sep 2021 15:28:06 +0000 (UTC) Date: Wed, 29 Sep 2021 23:28:01 +0800 From: Ming Lei To: Sagi Grimberg Cc: Jens Axboe , Christoph Hellwig , linux-block@vger.kernel.org, linux-nvme@lists.infradead.org, Keith Busch Subject: Re: [PATCH 4/5] nvme: paring quiesce/unquiesce Message-ID: References: <20210929041559.701102-1-ming.lei@redhat.com> <20210929041559.701102-5-ming.lei@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Wed, Sep 29, 2021 at 02:49:39PM +0300, Sagi Grimberg wrote: > > > On 9/29/21 7:15 AM, Ming Lei wrote: > > The current blk_mq_quiesce_queue() and blk_mq_unquiesce_queue() always > > stops and starts the queue unconditionally. And there can be concurrent > > quiesce/unquiesce coming from different unrelated code paths, so > > unquiesce may come unexpectedly and start queue too early. > > > > Prepare for supporting nested / concurrent quiesce/unquiesce, so that we > > can address the above issue. > > > > NVMe has very complicated quiesce/unquiesce use pattern, add one mutex > > and queue stopped state in nvme_ctrl, so that we can make sure that > > quiece/unquiesce is called in pair. > > > > Signed-off-by: Ming Lei > > --- > > drivers/nvme/host/core.c | 51 ++++++++++++++++++++++++++++++++++++---- > > drivers/nvme/host/nvme.h | 4 ++++ > > 2 files changed, 50 insertions(+), 5 deletions(-) > > > > diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c > > index 23fb746a8970..5d0b2eb38e43 100644 > > --- a/drivers/nvme/host/core.c > > +++ b/drivers/nvme/host/core.c > > @@ -4375,6 +4375,7 @@ int nvme_init_ctrl(struct nvme_ctrl *ctrl, struct device *dev, > > clear_bit(NVME_CTRL_FAILFAST_EXPIRED, &ctrl->flags); > > spin_lock_init(&ctrl->lock); > > mutex_init(&ctrl->scan_lock); > > + mutex_init(&ctrl->queues_stop_lock); > > INIT_LIST_HEAD(&ctrl->namespaces); > > xa_init(&ctrl->cels); > > init_rwsem(&ctrl->namespaces_rwsem); > > @@ -4450,14 +4451,44 @@ int nvme_init_ctrl(struct nvme_ctrl *ctrl, struct device *dev, > > } > > EXPORT_SYMBOL_GPL(nvme_init_ctrl); > > +static void __nvme_stop_admin_queue(struct nvme_ctrl *ctrl) > > +{ > > + lockdep_assert_held(&ctrl->queues_stop_lock); > > + > > + if (!ctrl->admin_queue_stopped) { > > + blk_mq_quiesce_queue(ctrl->admin_q); > > + ctrl->admin_queue_stopped = true; > > + } > > +} > > + > > +static void __nvme_start_admin_queue(struct nvme_ctrl *ctrl) > > +{ > > + lockdep_assert_held(&ctrl->queues_stop_lock); > > + > > + if (ctrl->admin_queue_stopped) { > > + blk_mq_unquiesce_queue(ctrl->admin_q); > > + ctrl->admin_queue_stopped = false; > > + } > > +} > > I'd make this a bit we can flip atomically. > > > + > > static void nvme_start_ns_queue(struct nvme_ns *ns) > > { > > - blk_mq_unquiesce_queue(ns->queue); > > + lockdep_assert_held(&ns->ctrl->queues_stop_lock); > > + > > + if (test_bit(NVME_NS_STOPPED, &ns->flags)) { > > + blk_mq_unquiesce_queue(ns->queue); > > + clear_bit(NVME_NS_STOPPED, &ns->flags); > > + } > > } > > static void nvme_stop_ns_queue(struct nvme_ns *ns) > > { > > - blk_mq_quiesce_queue(ns->queue); > > + lockdep_assert_held(&ns->ctrl->queues_stop_lock); > > + > > + if (!test_bit(NVME_NS_STOPPED, &ns->flags)) { > > + blk_mq_quiesce_queue(ns->queue); > > + set_bit(NVME_NS_STOPPED, &ns->flags); > > + } > > } > > Why not use test_and_set_bit/test_and_clear_bit for serialization? > > > /* > > @@ -4490,16 +4521,18 @@ void nvme_kill_queues(struct nvme_ctrl *ctrl) > > { > > struct nvme_ns *ns; > > + mutex_lock(&ctrl->queues_stop_lock); > > down_read(&ctrl->namespaces_rwsem); > > /* Forcibly unquiesce queues to avoid blocking dispatch */ > > if (ctrl->admin_q && !blk_queue_dying(ctrl->admin_q)) > > - nvme_start_admin_queue(ctrl); > > + __nvme_start_admin_queue(ctrl); > > list_for_each_entry(ns, &ctrl->namespaces, list) > > nvme_set_queue_dying(ns); > > up_read(&ctrl->namespaces_rwsem); > > + mutex_unlock(&ctrl->queues_stop_lock); > > This extra lock wrapping the namespaces_rwsem is scary. The > ordering rules are not clear to me. The rule is clear: queues_stop_lock has to be acquired before locking ->namespaces_rwsem. Using test_and_set_bit/test_and_clear_bit could be enough for pairing quiesce and unquiesce, I will try to remove the lock of ->queues_stop_lock in next version. Thanks, Ming