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=-4.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 7DC62C2D0CE for ; Fri, 24 Jan 2020 05:16:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4FDDB2071E for ; Fri, 24 Jan 2020 05:16:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579842966; bh=+bhb+s0f7B8ftjSnB2z/I4wHjcLdDMiVwk5zcTEu+Xg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=O5n9cc636D2Z3kUogtVx7y/25+QcnuP/w+4YADpigb0Nfkj07EfAJB/o6j6RFDhwy kRv6EBlznT1tD6eqEt7lW9s7T0wcCVw9Ed15NreKz9mJUnjBsd9csP5wPqAAWISf3x qaTcf4dfzVLNZJV2uUerMIyLCWWLXD5Q8EpIncsU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727384AbgAXFQD (ORCPT ); Fri, 24 Jan 2020 00:16:03 -0500 Received: from mail.kernel.org ([198.145.29.99]:33830 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727163AbgAXFQD (ORCPT ); Fri, 24 Jan 2020 00:16:03 -0500 Received: from sol.localdomain (c-107-3-166-239.hsd1.ca.comcast.net [107.3.166.239]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id BBDDF2071A; Fri, 24 Jan 2020 05:16:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579842963; bh=+bhb+s0f7B8ftjSnB2z/I4wHjcLdDMiVwk5zcTEu+Xg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=XDHBOOKK9bkcNNfisMo8Nc3n1utEsOSFcTbo/UH7ZqTVyKMQuk6ACT1kRFMpzt8aB 5j6gHRPkoqlU8SqTZZWXuXn9s/Hhoi+DtJXL/EC2pRIXpb26vbju+EHQM3laQjcWOM k7vSkMNunrddsoN4QHTjTyp+7TwQ5xYVI6swmAeo= Date: Thu, 23 Jan 2020 21:16:01 -0800 From: Eric Biggers To: Gao Xiang Cc: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, Alexander Viro , Daniel Rosenberg , Gabriel Krisman Bertazi Subject: Re: [PATCH] ext4: fix race conditions in ->d_compare() and ->d_hash() Message-ID: <20200124051601.GB832@sol.localdomain> References: <20200124041234.159740-1-ebiggers@kernel.org> <20200124050423.GA31271@hsiangkao-HP-ZHAN-66-Pro-G1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200124050423.GA31271@hsiangkao-HP-ZHAN-66-Pro-G1> Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Fri, Jan 24, 2020 at 01:04:25PM +0800, Gao Xiang wrote: > > diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c > > index 8964778aabefb..0129d14629881 100644 > > --- a/fs/ext4/dir.c > > +++ b/fs/ext4/dir.c > > @@ -671,9 +671,11 @@ static int ext4_d_compare(const struct dentry *dentry, unsigned int len, > > const char *str, const struct qstr *name) > > { > > struct qstr qstr = {.name = str, .len = len }; > > - struct inode *inode = dentry->d_parent->d_inode; > > + const struct dentry *parent = READ_ONCE(dentry->d_parent); > > I'm not sure if we really need READ_ONCE d_parent here (p.s. d_parent > won't be NULL anyway), and d_seq will guard all its validity. If I'm > wrong, correct me kindly... > > Otherwise, it looks good to me... > Reviewed-by: Gao Xiang > While d_parent can't be set to NULL, it can still be changed concurrently. So we need READ_ONCE() to ensure that a consistent value is used. - Eric