From patchwork Wed Oct 20 09:48:30 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "yebin (H)" X-Patchwork-Id: 12571903 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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 41D45C433EF for ; Wed, 20 Oct 2021 09:36:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 262C86112D for ; Wed, 20 Oct 2021 09:36:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230031AbhJTJiP (ORCPT ); Wed, 20 Oct 2021 05:38:15 -0400 Received: from szxga01-in.huawei.com ([45.249.212.187]:29917 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229555AbhJTJiO (ORCPT ); Wed, 20 Oct 2021 05:38:14 -0400 Received: from dggeme754-chm.china.huawei.com (unknown [172.30.72.55]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4HZ53050sczbnCM; Wed, 20 Oct 2021 17:31:24 +0800 (CST) Received: from huawei.com (10.175.127.227) by dggeme754-chm.china.huawei.com (10.3.19.100) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2308.15; Wed, 20 Oct 2021 17:35:57 +0800 From: Ye Bin To: , , , CC: , Ye Bin Subject: [PATCH -next] nbd: Fix hungtask when nbd_config_put Date: Wed, 20 Oct 2021 17:48:30 +0800 Message-ID: <20211020094830.3056325-1-yebin10@huawei.com> X-Mailer: git-send-email 2.31.1 MIME-Version: 1.0 X-Originating-IP: [10.175.127.227] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To dggeme754-chm.china.huawei.com (10.3.19.100) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org I got follow issue: [ 247.381177] INFO: task kworker/u10:0:47 blocked for more than 120 seconds. [ 247.382644] Not tainted 4.19.90-dirty #140 [ 247.383502] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 247.385027] Call Trace: [ 247.388384] schedule+0xb8/0x3c0 [ 247.388966] schedule_timeout+0x2b4/0x380 [ 247.392815] wait_for_completion+0x367/0x510 [ 247.397713] flush_workqueue+0x32b/0x1340 [ 247.402700] drain_workqueue+0xda/0x3c0 [ 247.403442] destroy_workqueue+0x7b/0x690 [ 247.405014] nbd_config_put.cold+0x2f9/0x5b6 [ 247.405823] recv_work+0x1fd/0x2b0 [ 247.406485] process_one_work+0x70b/0x1610 [ 247.407262] worker_thread+0x5a9/0x1060 [ 247.408699] kthread+0x35e/0x430 [ 247.410918] ret_from_fork+0x1f/0x30 We can reprodeuce issue as follows: 1. Inject memory fault in nbd_start_device @@ -1244,10 +1248,18 @@ static int nbd_start_device(struct nbd_device *nbd) nbd_dev_dbg_init(nbd); for (i = 0; i < num_connections; i++) { struct recv_thread_args *args; - - args = kzalloc(sizeof(*args), GFP_KERNEL); + + if (i == 1) { + args = NULL; + printk("%s: inject malloc error\n", __func__); + } + else + args = kzalloc(sizeof(*args), GFP_KERNEL); 2. Inject delay in recv_work @@ -757,6 +760,8 @@ static void recv_work(struct work_struct *work) blk_mq_complete_request(blk_mq_rq_from_pdu(cmd)); } + printk("%s: comm=%s pid=%d\n", __func__, current->comm, current->pid); + mdelay(5 * 1000); nbd_config_put(nbd); atomic_dec(&config->recv_threads); wake_up(&config->recv_wq); 3. Create nbd server nbd-server 8000 /tmp/disk 4. Create nbd client nbd-client localhost 8000 /dev/nbd1 Then will trigger above issue. Reason is when add delay in recv_work, lead to relase the last reference of 'nbd->config_refs'. nbd_config_put will call flush_workqueue to make all work finish. Obviously, it will lead to deadloop. To solve this issue, we must ensure 'recv_work' all exit before release the last 'nbd->config_refs' reference count. Signed-off-by: Ye Bin --- drivers/block/nbd.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index 0ee104fbb628..ba74887e24a8 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -2074,6 +2074,9 @@ static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info) set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags); refcount_inc(&nbd->config_refs); nbd_connect_reply(info, nbd->index); + } else if (nbd->recv_workq){ + sock_shutdown(nbd); + flush_workqueue(nbd->recv_workq); } nbd_config_put(nbd); if (put_dev)