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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 D56A1C432C3 for ; Fri, 15 Nov 2019 01:57:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ABC3920706 for ; Fri, 15 Nov 2019 01:57:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727387AbfKOB5X (ORCPT ); Thu, 14 Nov 2019 20:57:23 -0500 Received: from szxga07-in.huawei.com ([45.249.212.35]:50294 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726956AbfKOB5X (ORCPT ); Thu, 14 Nov 2019 20:57:23 -0500 Received: from DGGEMS406-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id CD7728AE8EE6C43EE20A; Fri, 15 Nov 2019 09:57:21 +0800 (CST) Received: from [127.0.0.1] (10.173.220.96) by DGGEMS406-HUB.china.huawei.com (10.3.19.206) with Microsoft SMTP Server id 14.3.439.0; Fri, 15 Nov 2019 09:57:14 +0800 Subject: Re: [PATCH] debugfs: fix potential infinite loop in debugfs_remove_recursive From: "yukuai (C)" To: Steven Rostedt CC: , , , , , , , , , "Al Viro" References: <1572528884-67565-1-git-send-email-yukuai3@huawei.com> <20191113151755.7125e914@gandalf.local.home> <20191113214307.29a8d001@oasis.local.home> <0ceb4529-5238-e7fc-2b5b-d2f0bdeb706e@huawei.com> <20191114093410.15f10eda@gandalf.local.home> <6ac793b1-5472-6a39-fe94-348ad6a4e2be@huawei.com> Message-ID: <9441c491-3d91-f16b-71fc-aeb658d6c8f0@huawei.com> Date: Fri, 15 Nov 2019 09:57:12 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <6ac793b1-5472-6a39-fe94-348ad6a4e2be@huawei.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.173.220.96] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2019/11/15 9:47, yukuai (C) 写道: > > > On 2019/11/14 22:34, Steven Rostedt wrote: >> On Thu, 14 Nov 2019 14:59:04 +0800 >> "yukuai (C)" wrote: >> >>>> Have you tried this patch with lockdep enabled and tried to hit this >>>> code path? >>>> >> >>> You are right, I get the results with lockdep enabled: >> >> That was what I was afraid of :-( >> >>> [   64.314748] ============================================ >>> [   64.315568] WARNING: possible recursive locking detected >>> [   64.316549] 5.4.0-rc7-dirty #5 Tainted: G           O >>> [   64.317398] -------------------------------------------- >>> [   64.318230] rmmod/2607 is trying to acquire lock: >> >>> >>> The warning will disappeare by adding >>> lockdep_set_novalidate_class(&child->d_lock) before calling >>> simple_empty(child). But I'm not sure It's the right modfication. >> >> I'm wondering if we should add a simple_empty_unlocked() that does >> simple_empty() without taking the lock, to allow us to call >> spin_lock_nested() on the child. Of course, I don't know how much >> nesting we allow as it calls the nesting too. > Do you think we can do this: > 1. add a new enum type for dentry_d_lock_class: > enum dentry_d_lock_class > { >     DENTRY_D_LOCK_NORMAL, /* implicitly used by plain spin_lock() APIs. */ >     DENTRY_D_LOCK_NESTED missing a ',' >     DENTRY_D_LOCK_NESTED_1 /* maybe another name */ > }; > 2. use the new enum type in simple_empty > int simple_empty(struct dentry *dentry) > { >     spin_lock(&dentry->d_lock, DENTRY_D_LOCK_NESTED); should be 'spin_lock_nested' >     list_for_each_entry(child, &dentry->d_subdirs, d_child) { >         spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED_1); > } > > If you agree, I'll try to send a patch or patchset(with modification in > debugfs_remove_recursive). sorry about the stupid mistake.. Thanks! Yu Kuai