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 X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 11A81C2D0CE for ; Wed, 22 Jan 2020 02:45:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CAA7B24655 for ; Wed, 22 Jan 2020 02:45:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728842AbgAVCpo (ORCPT ); Tue, 21 Jan 2020 21:45:44 -0500 Received: from szxga04-in.huawei.com ([45.249.212.190]:10125 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727141AbgAVCpo (ORCPT ); Tue, 21 Jan 2020 21:45:44 -0500 Received: from DGGEMS406-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id A014D63E922200D617CC; Wed, 22 Jan 2020 10:45:41 +0800 (CST) Received: from [127.0.0.1] (10.173.222.66) by DGGEMS406-HUB.china.huawei.com (10.3.19.206) with Microsoft SMTP Server id 14.3.439.0; Wed, 22 Jan 2020 10:45:40 +0800 Subject: Re: [PATCH] nbd: add a flush_workqueue in nbd_start_device To: Jens Axboe , Josef Bacik , CC: , , References: <20200121124813.13332-1-sunke32@huawei.com> <82a3eb7e-883c-a091-feec-27f3937491ab@toxicpanda.com> <83d21549-66a0-0e76-89e5-1303c5b19102@kernel.dk> From: "sunke (E)" Message-ID: Date: Wed, 22 Jan 2020 10:45:39 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: <83d21549-66a0-0e76-89e5-1303c5b19102@kernel.dk> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.173.222.66] X-CFilter-Loop: Reflected Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org 在 2020/1/22 5:25, Jens Axboe 写道: > On 1/21/20 7:00 AM, Josef Bacik wrote: >> On 1/21/20 7:48 AM, Sun Ke wrote: >>> When kzalloc fail, may cause trying to destroy the >>> workqueue from inside the workqueue. >>> >>> If num_connections is m (2 < m), and NO.1 ~ NO.n >>> (1 < n < m) kzalloc are successful. The NO.(n + 1) >>> failed. Then, nbd_start_device will return ENOMEM >>> to nbd_start_device_ioctl, and nbd_start_device_ioctl >>> will return immediately without running flush_workqueue. >>> However, we still have n recv threads. If nbd_release >>> run first, recv threads may have to drop the last >>> config_refs and try to destroy the workqueue from >>> inside the workqueue. >>> >>> To fix it, add a flush_workqueue in nbd_start_device. >>> >>> Fixes: e9e006f5fcf2 ("nbd: fix max number of supported devs") >>> Signed-off-by: Sun Ke >>> --- >>> drivers/block/nbd.c | 7 ++++++- >>> 1 file changed, 6 insertions(+), 1 deletion(-) >>> >>> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c >>> index b4607dd96185..dd1f8c2c6169 100644 >>> --- a/drivers/block/nbd.c >>> +++ b/drivers/block/nbd.c >>> @@ -1264,7 +1264,12 @@ static int nbd_start_device(struct nbd_device *nbd) >>> >>> args = kzalloc(sizeof(*args), GFP_KERNEL); >>> if (!args) { >>> - sock_shutdown(nbd); >>> + if (i == 0) >>> + sock_shutdown(nbd); >>> + else { >>> + sock_shutdown(nbd); >>> + flush_workqueue(nbd->recv_workq); >>> + } >> >> Just for readability sake why don't we just flush_workqueue() >> unconditionally, and add a comment so we know why in the future. > > Or maybe just make it: > > sock_shutdown(nbd); > if (i) > flush_workqueue(nbd->recv_workq); > > which does the same thing, but is still readable. The current code with > the shutdown duplication is just a bit odd. Needs a comment either way. > OK, I will improve it in my v2 patch. Thanks, Sun Ke