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 75D96C4167B for ; Tue, 28 Nov 2023 06:22:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343620AbjK1GWc (ORCPT ); Tue, 28 Nov 2023 01:22:32 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33216 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232615AbjK1GW3 (ORCPT ); Tue, 28 Nov 2023 01:22:29 -0500 Received: from out30-101.freemail.mail.aliyun.com (out30-101.freemail.mail.aliyun.com [115.124.30.101]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6BC9E183 for ; Mon, 27 Nov 2023 22:22:35 -0800 (PST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R101e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046050;MF=yaoma@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0VxJbmTM_1701152551; Received: from 30.178.66.233(mailfrom:yaoma@linux.alibaba.com fp:SMTPD_---0VxJbmTM_1701152551) by smtp.aliyun-inc.com; Tue, 28 Nov 2023 14:22:33 +0800 Message-ID: <65b0c372-b308-46dd-c2f2-a5ddb50adb10@linux.alibaba.com> Date: Tue, 28 Nov 2023 14:22:27 +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 Cc: axboe@kernel.dk, hch@lst.de, sagi@grimberg.me, 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> 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 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. On 2023/11/28 02:07, Keith Busch wrote: > On Thu, Nov 23, 2023 at 07:00:13PM +0800, Bitao Hu wrote: >> @@ -3631,6 +3631,11 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, struct nvme_ns_info *info) >> goto out_unlink_ns; >> >> down_write(&ctrl->namespaces_rwsem); >> + /* preventing adding ns during resetting */ >> + if (unlikely(ctrl->state != NVME_CTRL_LIVE)) { > > We can't rely on ctrl->state for preventing deadlocks. Reading unlocked > ctrl->state is often used, but should be considered advisory-only since > the state could change immediatly after reading it. > >> + up_write(&ctrl->namespaces_rwsem); >> + goto out_unlink_ns; >> + } >> nvme_ns_add_to_ctrl_list(ns); >> up_write(&ctrl->namespaces_rwsem); >> nvme_get_ctrl(ctrl);