From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keith Busch Subject: Re: [PATCH 11/12] nvme: Use BLK_MQ_S_STOPPED instead of QUEUE_FLAG_STOPPED in blk-mq code Date: Fri, 28 Oct 2016 12:01:45 -0400 Message-ID: <20161028160145.GC5621@localhost.localdomain> References: <805e1911-cd10-0563-c76b-256d76054b08@sandisk.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mga05.intel.com ([192.55.52.43]:53357 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752947AbcJ1PvB (ORCPT ); Fri, 28 Oct 2016 11:51:01 -0400 Content-Disposition: inline In-Reply-To: <805e1911-cd10-0563-c76b-256d76054b08@sandisk.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Bart Van Assche Cc: Jens Axboe , Christoph Hellwig , James Bottomley , "Martin K. Petersen" , Mike Snitzer , Doug Ledford , Ming Lei , Laurence Oberman , "linux-block@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "linux-rdma@vger.kernel.org" , "linux-nvme@lists.infradead.org" On Wed, Oct 26, 2016 at 03:56:04PM -0700, Bart Van Assche wrote: > diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c > index 7bb73ba..b662416 100644 > --- a/drivers/nvme/host/core.c > +++ b/drivers/nvme/host/core.c > @@ -205,7 +205,7 @@ void nvme_requeue_req(struct request *req) > > blk_mq_requeue_request(req, false); > spin_lock_irqsave(req->q->queue_lock, flags); > - if (!blk_queue_stopped(req->q)) > + if (!blk_mq_queue_stopped(req->q)) > blk_mq_kick_requeue_list(req->q); > spin_unlock_irqrestore(req->q->queue_lock, flags); > } > @@ -2079,10 +2079,6 @@ void nvme_stop_queues(struct nvme_ctrl *ctrl) > > mutex_lock(&ctrl->namespaces_mutex); > list_for_each_entry(ns, &ctrl->namespaces, list) { > - spin_lock_irq(ns->queue->queue_lock); > - queue_flag_set(QUEUE_FLAG_STOPPED, ns->queue); > - spin_unlock_irq(ns->queue->queue_lock); > - > blk_mq_cancel_requeue_work(ns->queue); > blk_mq_stop_hw_queues(ns->queue); There's actually a reason the queue stoppage is using a different flag than blk_mq_queue_stopped: kicking the queue starts stopped queues. The driver has to ensure the requeue work can't be kicked prior to cancelling the current requeue work. Once we know requeue work isn't running and can't restart again, then we're safe to stop the hw queues. It's a pretty obscure condition, requiring the controller post an error completion at the same time the driver decides to reset the controller. Here's the sequence with the wrong outcome: CPU A CPU B ----- ----- nvme_stop_queues nvme_requeue_req blk_mq_stop_hw_queues if (blk_mq_queue_stopped) <- returns false blk_mq_stop_hw_queue blk_mq_kick_requeue_list blk_mq_requeue_work blk_mq_start_hw_queues