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 D5CAAC433EF for ; Tue, 28 Dec 2021 07:48:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235385AbhL1HsR (ORCPT ); Tue, 28 Dec 2021 02:48:17 -0500 Received: from szxga02-in.huawei.com ([45.249.212.188]:29298 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235367AbhL1HsQ (ORCPT ); Tue, 28 Dec 2021 02:48:16 -0500 Received: from kwepemi100003.china.huawei.com (unknown [172.30.72.54]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4JNRTZ2K3mzbjgS; Tue, 28 Dec 2021 15:47:46 +0800 (CST) Received: from kwepemm600013.china.huawei.com (7.193.23.68) by kwepemi100003.china.huawei.com (7.221.188.122) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.20; Tue, 28 Dec 2021 15:48:14 +0800 Received: from [10.174.178.46] (10.174.178.46) by kwepemm600013.china.huawei.com (7.193.23.68) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.20; Tue, 28 Dec 2021 15:48:13 +0800 Subject: Re: [PATCH -next V3] ubi: fix race condition between ctrl_cdev_ioctl and ubi_cdev_ioctl To: Richard Weinberger , "libaokun (A)" CC: Miquel Raynal , Vignesh Raghavendra , linux-mtd , linux-kernel , , Hulk Robot References: <20211105093022.1360601-1-libaokun1@huawei.com> <7e00eda5-3b35-6d3c-29fb-664b12cca6dd@huawei.com> <509065063.197038.1640293568550.JavaMail.zimbra@nod.at> From: Zhihao Cheng Message-ID: Date: Tue, 28 Dec 2021 15:48:12 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <509065063.197038.1640293568550.JavaMail.zimbra@nod.at> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.178.46] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To kwepemm600013.china.huawei.com (7.193.23.68) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2021/12/24 5:06, Richard Weinberger 写道: > ----- Ursprüngliche Mail ----- >>> ubi_get_device is used to prevent devices from being deleted during >>> sysfs execution. However, now kernfs ensures that devices will not >>> be deleted before all reference counting are released. >>> The key process is shown in the following stack. > > ubi_get_device() in dev_attribute_show() is used to detect whether > the ubi device got detached while the sysfs file is open. > > Hmm. I thought for sysfs this is not the case since sysfs does not implement > a release() method. So kernfs_drain_open_files() will return early. > But there is a good chance that I don't got all kernfs/sysfs details. > kernfs_drain() will wait 'root->deactivate_waitq' if atomic_read(&kn->active) not equals to KN_DEACTIVATED_BIAS. The UBI seq_show callback is invoked with avtive cnt taken: vfs_read kernfs_fop_read_iter seq_read_iter m->op->start (kernfs_seq_start) // kernfs_get_active(of->kn) kernfs_seq_show dev_attribute_show [ubi] m->op->stop (kernfs_seq_stop) // kernfs_put_active(of->kn) The kernfs_drain() is stuck at wait_event() until sysfs reading finished, in my local test.