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=-6.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,T_DKIMWL_WL_HIGH,USER_AGENT_GIT 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 24F57C282DD for ; Thu, 23 May 2019 19:24:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EFD3A2186A for ; Thu, 23 May 2019 19:24:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1558639473; bh=YzxVZagn4yBuXs8rIInrK+XHSs1m65ndjNkEB/hNnqw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=O7NP0v5vjDNd3k8oO0SdhbpZ8P6ZMB/phAg9NP5R9tD9IOAsUdCJRhH89QXSNY48m C0fHU3tuGsS/2DP97dwLeocUKLPXgJBmVi7D3INhOEci1GzD0sZrJsMoKr4D5mPyOI SSg9cGmJXmJPsfhaMShFv86ii4tDMUnY1Bpg6NJ8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390923AbfEWTYc (ORCPT ); Thu, 23 May 2019 15:24:32 -0400 Received: from mail.kernel.org ([198.145.29.99]:35474 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390434AbfEWTY3 (ORCPT ); Thu, 23 May 2019 15:24:29 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 9EBEF21872; Thu, 23 May 2019 19:24:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1558639468; bh=YzxVZagn4yBuXs8rIInrK+XHSs1m65ndjNkEB/hNnqw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=o/p6J1/R0CsJPKQ8b4b4DIuWJzFBacTvZ3ZYO83a835ifb9CbtgrLbUxxrKbefTgD BDCtVBDpbVCMJRob10MpnJpIUaaM2RuvjJmRBB1FTmnJco+r8BtaxDlBx70nAVxWwK C0tpESgxdgWPikxQY1kwzHBcW0yzCWAFASHSCeOE= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Kirill Smelkov , Miklos Szeredi Subject: [PATCH 5.0 099/139] fuse: Add FOPEN_STREAM to use stream_open() Date: Thu, 23 May 2019 21:06:27 +0200 Message-Id: <20190523181733.421233135@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190523181720.120897565@linuxfoundation.org> References: <20190523181720.120897565@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Kirill Smelkov commit bbd84f33652f852ce5992d65db4d020aba21f882 upstream. Starting from commit 9c225f2655e3 ("vfs: atomic f_pos accesses as per POSIX") files opened even via nonseekable_open gate read and write via lock and do not allow them to be run simultaneously. This can create read vs write deadlock if a filesystem is trying to implement a socket-like file which is intended to be simultaneously used for both read and write from filesystem client. See commit 10dce8af3422 ("fs: stream_open - opener for stream-like files so that read and write can run simultaneously without deadlock") for details and e.g. commit 581d21a2d02a ("xenbus: fix deadlock on writes to /proc/xen/xenbus") for a similar deadlock example on /proc/xen/xenbus. To avoid such deadlock it was tempting to adjust fuse_finish_open to use stream_open instead of nonseekable_open on just FOPEN_NONSEEKABLE flags, but grepping through Debian codesearch shows users of FOPEN_NONSEEKABLE, and in particular GVFS which actually uses offset in its read and write handlers https://codesearch.debian.net/search?q=-%3Enonseekable+%3D https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1080 https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1247-1346 https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1399-1481 so if we would do such a change it will break a real user. Add another flag (FOPEN_STREAM) for filesystem servers to indicate that the opened handler is having stream-like semantics; does not use file position and thus the kernel is free to issue simultaneous read and write request on opened file handle. This patch together with stream_open() should be added to stable kernels starting from v3.14+. This will allow to patch OSSPD and other FUSE filesystems that provide stream-like files to return FOPEN_STREAM | FOPEN_NONSEEKABLE in open handler and this way avoid the deadlock on all kernel versions. This should work because fuse_finish_open ignores unknown open flags returned from a filesystem and so passing FOPEN_STREAM to a kernel that is not aware of this flag cannot hurt. In turn the kernel that is not aware of FOPEN_STREAM will be < v3.14 where just FOPEN_NONSEEKABLE is sufficient to implement streams without read vs write deadlock. Cc: stable@vger.kernel.org # v3.14+ Signed-off-by: Kirill Smelkov Signed-off-by: Miklos Szeredi Signed-off-by: Greg Kroah-Hartman --- fs/fuse/file.c | 4 +++- include/uapi/linux/fuse.h | 2 ++ 2 files changed, 5 insertions(+), 1 deletion(-) --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -181,7 +181,9 @@ void fuse_finish_open(struct inode *inod file->f_op = &fuse_direct_io_file_operations; if (!(ff->open_flags & FOPEN_KEEP_CACHE)) invalidate_inode_pages2(inode->i_mapping); - if (ff->open_flags & FOPEN_NONSEEKABLE) + if (ff->open_flags & FOPEN_STREAM) + stream_open(inode, file); + else if (ff->open_flags & FOPEN_NONSEEKABLE) nonseekable_open(inode, file); if (fc->atomic_o_trunc && (file->f_flags & O_TRUNC)) { struct fuse_inode *fi = get_fuse_inode(inode); --- a/include/uapi/linux/fuse.h +++ b/include/uapi/linux/fuse.h @@ -226,11 +226,13 @@ struct fuse_file_lock { * FOPEN_KEEP_CACHE: don't invalidate the data cache on open * FOPEN_NONSEEKABLE: the file is not seekable * FOPEN_CACHE_DIR: allow caching this directory + * FOPEN_STREAM: the file is stream-like (no file position at all) */ #define FOPEN_DIRECT_IO (1 << 0) #define FOPEN_KEEP_CACHE (1 << 1) #define FOPEN_NONSEEKABLE (1 << 2) #define FOPEN_CACHE_DIR (1 << 3) +#define FOPEN_STREAM (1 << 4) /** * INIT request/reply flags