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=-7.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,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 5D58EC433FE for ; Sun, 6 Dec 2020 20:54:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 282422224C for ; Sun, 6 Dec 2020 20:54:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728095AbgLFUyQ (ORCPT ); Sun, 6 Dec 2020 15:54:16 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47238 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726780AbgLFUyP (ORCPT ); Sun, 6 Dec 2020 15:54:15 -0500 Received: from nautica.notk.org (ipv6.notk.org [IPv6:2001:41d0:1:7a93::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6188CC0613D1; Sun, 6 Dec 2020 12:53:35 -0800 (PST) Received: by nautica.notk.org (Postfix, from userid 1001) id 8F6EAC009; Sun, 6 Dec 2020 21:53:33 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=codewreck.org; s=2; t=1607288013; bh=JjaOew6og4Ma3TgZ9+cKOV5nQwdt07PsMK9VaipXVXo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Kw6fVZE2HDNIfSU4yQYDOZlyGHncJmSp4+Jf44efQ5j7AT+fE6r0aQVT1r2BhqUz6 LZQ/u8PAEbDqZmCHgAspLQz3CpX0rk/MaK3/+/O9xGR18Mno8u9JUthL3u9hmA1uZZ p8JfHQ/U32MAbrXSv3lycm2ZVNDUwAtZ+zL1jepJJugl15k+idutduhvMHAzfgMbZT ihzPwkWRiJsLja4h9QVgG4Y8OIprN+oXUqqjTttowPdV0u+6Kps3dLKvsWhSkZ3hDt IMP+MG98XZtfupvzwulKtCCkw4eJhnbWgHKDuXoF7gXGZxXC/LwMfEsZ2oWoyWmVn9 ryiZIMcKj6Wng== Date: Sun, 6 Dec 2020 21:53:18 +0100 From: Dominique Martinet To: Chengguang Xu Cc: ericvh@gmail.com, lucho@ionkov.net, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, v9fs-developer@lists.sourceforge.net Subject: Re: [V9fs-developer] [RFC PATCH] 9p: create writeback fid on shared mmap Message-ID: <20201206205318.GA25257@nautica> References: <20201205130904.518104-1-cgxu519@mykernel.net> <20201206091618.GA22629@nautica> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20201206091618.GA22629@nautica> User-Agent: Mutt/1.5.21 (2010-09-15) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Dominique Martinet wrote on Sun, Dec 06, 2020: > Chengguang Xu wrote on Sat, Dec 05, 2020: > > If vma is shared and the file was opened for writing, > > we should also create writeback fid because vma may be > > mprotected writable even if now readonly. > > Hm, I guess it makes sense. I had a second look, and generic_file_readonly_mmap uses vma's `vma->vm_flags & VM_MAYWRITE` instead (together with VM_SHARED), while mapping_writably_mapped ultimately basically only seems to validate that the mapping is shared from a look at mapping_map_writable callers? It's not very clear to me. OTOH, VM_MAYWRITE is set anytime we have a shared map where file has been opened read-write, which seems to be what you want with regards to protecting from mprotect calls. How about simply changing check from WRITE to MAYWRITE? v9inode = V9FS_I(inode); mutex_lock(&v9inode->v_mutex); if (!v9inode->writeback_fid && (vma->vm_flags & VM_SHARED) && - (vma->vm_flags & VM_WRITE)) { + (vma->vm_flags & VM_MAYWRITE)) { /* * clone a fid and add it to writeback_fid * we do it during mmap instead of -- Dominique