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 E6580C07E98 for ; Wed, 29 Nov 2023 03:30:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230251AbjK2D2v (ORCPT ); Tue, 28 Nov 2023 22:28:51 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38164 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229880AbjK2D2t (ORCPT ); Tue, 28 Nov 2023 22:28:49 -0500 Received: from out30-113.freemail.mail.aliyun.com (out30-113.freemail.mail.aliyun.com [115.124.30.113]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 734BE1AD for ; Tue, 28 Nov 2023 19:28:48 -0800 (PST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R501e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046060;MF=yaoma@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0VxMeem7_1701228524; Received: from 30.178.67.199(mailfrom:yaoma@linux.alibaba.com fp:SMTPD_---0VxMeem7_1701228524) by smtp.aliyun-inc.com; Wed, 29 Nov 2023 11:28:46 +0800 Message-ID: Date: Wed, 29 Nov 2023 11:28:40 +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: Sagi Grimberg , Keith Busch 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 On 2023/11/28 18:13, 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. > I think your proposal is nice, and I will test it. > 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).