From patchwork Sun Jun 9 14:39:09 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kirill Smelkov X-Patchwork-Id: 10983721 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id ACB1F14C0 for ; Sun, 9 Jun 2019 14:54:17 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 953CB2876D for ; Sun, 9 Jun 2019 14:54:17 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 871092882F; Sun, 9 Jun 2019 14:54:17 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.6 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI,URIBL_GREY autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 032482876D for ; Sun, 9 Jun 2019 14:54:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729043AbfFIOyN (ORCPT ); Sun, 9 Jun 2019 10:54:13 -0400 Received: from mail180-16.suw31.mandrillapp.com ([198.2.180.16]:12269 "EHLO mail180-16.suw31.mandrillapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728746AbfFIOyN (ORCPT ); Sun, 9 Jun 2019 10:54:13 -0400 X-Greylist: delayed 902 seconds by postgrey-1.27 at vger.kernel.org; Sun, 09 Jun 2019 10:54:12 EDT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; s=mandrill; d=nexedi.com; h=From:Subject:To:Cc:Message-Id:In-Reply-To:References:Date:MIME-Version:Content-Type:Content-Transfer-Encoding; i=kirr@nexedi.com; bh=dm0aK3M64H+SXVlIii//Ha6Kj1rTeiHz47q5OrGWw5I=; b=kZ5zWNL796wzCwTeQz9ViOb9CBjWjun7cJdcspxset2+Md1lSvFaYuSg3OXRTC+dlTN1v/9w8GL2 gzJ08I51Ez2mb1eEMVoRb15Cw0Y4Un2CduG4RQjBUFPPKlpkH7LiDMgkUn/05QMVEiWnIPbjzXPl mVCIB8j+Rpsgkj5aQ9U= Received: from pmta03.mandrill.prod.suw01.rsglab.com (127.0.0.1) by mail180-16.suw31.mandrillapp.com id hvkep822sc0l for ; Sun, 9 Jun 2019 14:39:09 +0000 (envelope-from ) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mandrillapp.com; i=@mandrillapp.com; q=dns/txt; s=mandrill; t=1560091149; h=From : Subject : To : Cc : Message-Id : In-Reply-To : References : Date : MIME-Version : Content-Type : Content-Transfer-Encoding : From : Subject : Date : X-Mandrill-User : List-Unsubscribe; bh=dm0aK3M64H+SXVlIii//Ha6Kj1rTeiHz47q5OrGWw5I=; b=SK6n7BkrQ7bW3iiqeEWXr+sUDHZO6cdmZJVP9TZU3z4enYUXQeR6fqDDaPXApV5OS5nUES gdHqF9V9vvjoWAZAnfIsdQK1I/pzApg3no0aPDquf7OSOaM/H7oDuoWr+HBNhF5Dx0Nl4BaP mkgRRSnLZLQ2e7Y97njMr+VfLuN0c= From: Kirill Smelkov Subject: [PATCH 3.16 2/2] fuse: Add FOPEN_STREAM to use stream_open() Received: from [87.98.221.171] by mandrillapp.com id 3b3930b96aaf4478bdbbd0307d3ac348; Sun, 09 Jun 2019 14:39:09 +0000 X-Mailer: git-send-email 2.20.1 To: , Ben Hutchings Cc: Sasha Levin , Greg Kroah-Hartman , Linus Torvalds , Miklos Szeredi , , , Kirill Smelkov , Miklos Szeredi Message-Id: <20190609135607.9840-3-kirr@nexedi.com> In-Reply-To: <20190609135607.9840-1-kirr@nexedi.com> References: <20190609135607.9840-1-kirr@nexedi.com> X-Report-Abuse: Please forward a copy of this message, including all headers, to abuse@mandrill.com X-Report-Abuse: You can also report abuse here: http://mandrillapp.com/contact/abuse?id=31050260.3b3930b96aaf4478bdbbd0307d3ac348 X-Mandrill-User: md_31050260 Date: Sun, 09 Jun 2019 14:39:09 +0000 MIME-Version: 1.0 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP 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 --- fs/fuse/file.c | 4 +++- include/uapi/linux/fuse.h | 2 ++ 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/fs/fuse/file.c b/fs/fuse/file.c index bc8f5de48fd9..69e471b042a6 100644 --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -214,7 +214,9 @@ void fuse_finish_open(struct inode *inode, struct file *file) 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); diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h index 25084a052a1e..cff91b018953 100644 --- a/include/uapi/linux/fuse.h +++ b/include/uapi/linux/fuse.h @@ -205,10 +205,12 @@ struct fuse_file_lock { * FOPEN_DIRECT_IO: bypass page cache for this open file * FOPEN_KEEP_CACHE: don't invalidate the data cache on open * FOPEN_NONSEEKABLE: the file is not seekable + * 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_STREAM (1 << 4) /** * INIT request/reply flags