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 180D9C4167B for ; Wed, 29 Nov 2023 09:24:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229834AbjK2JYN (ORCPT ); Wed, 29 Nov 2023 04:24:13 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52502 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229535AbjK2JYK (ORCPT ); Wed, 29 Nov 2023 04:24:10 -0500 Received: from out30-131.freemail.mail.aliyun.com (out30-131.freemail.mail.aliyun.com [115.124.30.131]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8148710E2 for ; Wed, 29 Nov 2023 01:24:15 -0800 (PST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R191e4;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=8;SR=0;TI=SMTPD_---0VxNaj96_1701249851; Received: from 30.178.67.199(mailfrom:yaoma@linux.alibaba.com fp:SMTPD_---0VxNaj96_1701249851) by smtp.aliyun-inc.com; Wed, 29 Nov 2023 17:24:12 +0800 Message-ID: <7a1a6a34-019a-3ecc-3aee-1a92d29eb6e9@linux.alibaba.com> Date: Wed, 29 Nov 2023 17:24:07 +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 From: yaoma Subject: Re: [PATCH] nvme: fix deadlock between reset and scan To: Sagi Grimberg Cc: axboe@kernel.dk, hch@lst.de, linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, kanie@linux.alibaba.com, Keith Busch , yaoma@linux.alibaba.com References: <1700737213-110685-1-git-send-email-yaoma@linux.alibaba.com> <65b0c372-b308-46dd-c2f2-a5ddb50adb10@linux.alibaba.com> Content-Language: en-US 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, Sagi Grimberg I revised my code following your advice and carried out tests. Test Scripts: for ((t=1;t<=128;t++)) do nsid=`nvme create-ns /dev/nvme0 -s 1453772 -c 1453772 -f 0\ -m 0 -d 0 | awk -F: '{print($NF);}'` nvme attach-ns /dev/nvme0 -n $nsid -c 0 done echo "resetting" nvme reset /dev/nvme0 lsblk | grep nvme0 | wc -l sleep 2 lsblk | grep nvme0 | wc -l Results: ... attach-ns: Success, nsid:128 resetting 23 128 After the fix, we will not be deadlocked. I find a minor issue. In the resetting state, the scan may not recognize all ns, but since a scan work is queued at the end of reset, so the impact is not significant. After the reset is completed, all ns can eventually be recognized. --- diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c index 21783aa2e..e361aba39 100644 --- a/drivers/nvme/host/core.c +++ b/drivers/nvme/host/core.c @@ -3630,6 +3630,10 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, struct nvme_ns_info *info) goto out_unlink_ns; down_write(&ctrl->namespaces_rwsem); + if (test_bit(NVME_CTRL_FROZEN, &ctrl->flags)) { + 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); @@ -4539,6 +4543,7 @@ void nvme_unfreeze(struct nvme_ctrl *ctrl) list_for_each_entry(ns, &ctrl->namespaces, list) blk_mq_unfreeze_queue(ns->queue); up_read(&ctrl->namespaces_rwsem); + clear_bit(NVME_CTRL_FROZEN, &ctrl->flags); } EXPORT_SYMBOL_GPL(nvme_unfreeze); @@ -4572,6 +4577,7 @@ void nvme_start_freeze(struct nvme_ctrl *ctrl) { struct nvme_ns *ns; + set_bit(NVME_CTRL_FROZEN, &ctrl->flags); down_read(&ctrl->namespaces_rwsem); list_for_each_entry(ns, &ctrl->namespaces, list) blk_freeze_queue_start(ns->queue); diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h index f35647c47..755319b0d 100644 --- a/drivers/nvme/host/nvme.h +++ b/drivers/nvme/host/nvme.h @@ -251,6 +251,7 @@ enum nvme_ctrl_flags { NVME_CTRL_STOPPED = 3, NVME_CTRL_SKIP_ID_CNS_CS = 4, NVME_CTRL_DIRTY_CAPABILITY = 5, + NVME_CTRL_FROZEN = 6, }; struct nvme_ctrl { -- 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. > > 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).