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=-9.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,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 161F0C43381 for ; Tue, 26 Mar 2019 23:37:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C771620811 for ; Tue, 26 Mar 2019 23:37:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=nexedi.com header.i=kirr@nexedi.com header.b="INtlbxYo"; dkim=pass (1024-bit key) header.d=mandrillapp.com header.i=@mandrillapp.com header.b="YcMOIyRo" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732800AbfCZXhQ (ORCPT ); Tue, 26 Mar 2019 19:37:16 -0400 Received: from mail128-16.atl41.mandrillapp.com ([198.2.128.16]:59615 "EHLO mail128-16.atl41.mandrillapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730333AbfCZXhP (ORCPT ); Tue, 26 Mar 2019 19:37:15 -0400 X-Greylist: delayed 902 seconds by postgrey-1.27 at vger.kernel.org; Tue, 26 Mar 2019 19:37:14 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=QL99GUss+MVS3eCKqjgk6p3ckRJUrMSLnzdhSyvE7f4=; b=INtlbxYoTwP35GWsscKvgX4FH6Cb3L3AoMLHtr3N1aTybhsxhn5iMZwe9wASJUai4TaH2BWq7atu kK5yoSv/8i710YL1GVQ9yFD5IbT5NxCpf002ipZSOHeVdHsxBZUzw6lFzEblQpLRMvr5ScPByZSx 44C1x/1yZMBn/9klzLI= Received: from pmta01.mandrill.prod.atl01.rsglab.com (127.0.0.1) by mail128-16.atl41.mandrillapp.com id hjarqk1mqukq for ; Tue, 26 Mar 2019 23:22:12 +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=1553642532; 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=QL99GUss+MVS3eCKqjgk6p3ckRJUrMSLnzdhSyvE7f4=; b=YcMOIyRoxP9g3Du+zMIOVDEKM1xToHFT0aYnfq96H4nKyWlArB2FXjoAgweDdsUGafloSv dWWDax5fTG7G8sI8hZRn24RsbVSK63whXeSJmguoiE5qj9q3taIFsCUjEBHuRjLjkod3qQJ6 U/aqnELpzFeyE7a0BCsOIekubXMW8= From: Kirill Smelkov Subject: [PATCH 3/3] fuse: Add FOPEN_STREAM and use stream_open() if filesystem returned that from open handler Received: from [87.98.221.171] by mandrillapp.com id cfa380936c2c47eaacb995baa539f9ea; Tue, 26 Mar 2019 23:22:12 +0000 X-Mailer: git-send-email 2.21.0.392.gf8f6787159 To: Miklos Szeredi Cc: , , Kirill Smelkov , Al Viro , Linus Torvalds , Michael Kerrisk , Yongzhi Pan , Jonathan Corbet , David Vrabel , Juergen Gross , Tejun Heo , Kirill Tkhai , Arnd Bergmann , Christoph Hellwig , Greg Kroah-Hartman , Julia Lawall , Nikolaus Rath , Han-Wen Nienhuys Message-Id: In-Reply-To: References: 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.cfa380936c2c47eaacb995baa539f9ea X-Mandrill-User: md_31050260 Date: Tue, 26 Mar 2019 23:22:12 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Starting from 9c225f2655 (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 previous patch "fs: stream_open - opener for stream-like files so that read and write can run simultaneously without deadlock" for details and e.g. 581d21a2d0 (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 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+ (the kernel where 9c225f2655 first appeared). 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: Al Viro Cc: Linus Torvalds Cc: Michael Kerrisk Cc: Yongzhi Pan Cc: Jonathan Corbet Cc: David Vrabel Cc: Juergen Gross Cc: Tejun Heo Cc: Kirill Tkhai Cc: Arnd Bergmann Cc: Christoph Hellwig Cc: Greg Kroah-Hartman Cc: Julia Lawall Cc: Nikolaus Rath Cc: Han-Wen Nienhuys Signed-off-by: Kirill Smelkov --- 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 ffaffe18352a..7ea4099cde16 100644 --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -181,7 +181,9 @@ 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 b4967d48bfda..93ac72a1e4ff 100644 --- 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 */ #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 -- 2.21.0.392.gf8f6787159