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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DF545C4167B for ; Wed, 29 Nov 2023 03:23:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234566AbjK2DXT (ORCPT ); Tue, 28 Nov 2023 22:23:19 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53978 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230469AbjK2DXM (ORCPT ); Tue, 28 Nov 2023 22:23:12 -0500 Received: from out30-110.freemail.mail.aliyun.com (out30-110.freemail.mail.aliyun.com [115.124.30.110]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C4A6A1BD0 for ; Tue, 28 Nov 2023 19:23:18 -0800 (PST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R781e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046056;MF=yaoma@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0VxMecw4_1701228195; Received: from 30.178.67.199(mailfrom:yaoma@linux.alibaba.com fp:SMTPD_---0VxMecw4_1701228195) by smtp.aliyun-inc.com; Wed, 29 Nov 2023 11:23:16 +0800 Message-ID: <6430641c-0db3-d9c2-4b75-51c179c52e8d@linux.alibaba.com> Date: Wed, 29 Nov 2023 11:23:13 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 Subject: Re: [PATCH] nvme: fix deadlock between reset and scan Content-Language: en-US To: Keith Busch , Sagi Grimberg Cc: axboe@kernel.dk, hch@lst.de, linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, kanie@linux.alibaba.com References: <1700737213-110685-1-git-send-email-yaoma@linux.alibaba.com> <65b0c372-b308-46dd-c2f2-a5ddb50adb10@linux.alibaba.com> From: yaoma In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I have previously tried the method that you proposed, and it could solve the deadlock issue. My worry is that if an I/O timeout occurs during the scan, it will trigger a reset. However, the reset will wait for the scan to end, which could introduce a new risk of deadlock. I agree with the suggestion made by Sagi Grimberg that this approach does not introduce new problems. On 2023/11/29 02:00, Keith Busch wrote: > On Tue, Nov 28, 2023 at 12:13:59PM +0200, Sagi Grimberg wrote: >> >> >> On 11/28/23 08:22, yaoma wrote: >>> Hi Keith Busch >>> >>> Thanks for your reply. >>> >>> The idea to avoid such a deadlock between nvme_reset and nvme_scan is to >>> ensure that no namespace can be added to ctrl->namespaces after >>> nvme_start_freeze has already been called. We can achieve this goal by >>> assessing the ctrl->state after we have already acquired the >>> ctrl->namespaces_rwsem lock, to decide whether to add the namespace to >>> the list or not. >>> 1. After we determine that ctrl->state is LIVE, it may be immediately >>> changed to another state. However, since we have already acquired the >>> lock, other tasks cannot access ctrl->namespace, so we can still safely >>> add the namespace to the list. After acquiring the lock, >>> nvme_start_freeze will freeze all ns->q in the list, including any newly >>> added namespaces. >>> 2. Before the completion of nvme_reset, ctrl->state will not be changed >>> to LIVE, so we will not add any more namespaces to the list. All ns->q >>> in the list is frozen, so nvme_wait_freeze can exit normally. >> >> I agree with the analysis, there is a hole between start_freeze and >> freeze_wait that a scan may add a ns to the ctrl ns list. >> >> However the fix should be to mark the ctrl with say NVME_CTRL_FROZEN >> flag set in nvme_freeze_start and cleared in nvme_unfreeze (similar >> to what we did with quiesce). Then the scan can check it before adding >> the new namespace (under the namespaces_rwsem). > > Could we just make sure that scan_work isn't running? If we reset a live > controller, then we're not depending on reset_work to unblock scan_work, > and can let scan_work end gracefully. The scan_work can't be rescheduled > again while in the resetting state. > > --- > diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c > index fad4cccce745c..5d6305475bad5 100644 > --- a/drivers/nvme/host/pci.c > +++ b/drivers/nvme/host/pci.c > @@ -2701,8 +2701,10 @@ static void nvme_reset_work(struct work_struct *work) > * If we're called to reset a live controller first shut it down before > * moving on. > */ > - if (dev->ctrl.ctrl_config & NVME_CC_ENABLE) > + if (dev->ctrl.ctrl_config & NVME_CC_ENABLE) { > + flush_work(&dev->ctrl.scan_work); > nvme_dev_disable(dev, false); > + } > nvme_sync_queues(&dev->ctrl); > > mutex_lock(&dev->shutdown_lock); > --