From patchwork Tue Mar 26 23:22:12 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kirill Smelkov X-Patchwork-Id: 10872313 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 79E67139A for ; Tue, 26 Mar 2019 23:37:21 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 55B3328B9F for ; Tue, 26 Mar 2019 23:37:21 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 461C328CBC; Tue, 26 Mar 2019 23:37:21 +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 8F82428B9F for ; Tue, 26 Mar 2019 23:37:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732802AbfCZXhS (ORCPT ); Tue, 26 Mar 2019 19:37:18 -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 S1731483AbfCZXhR (ORCPT ); Tue, 26 Mar 2019 19:37:17 -0400 X-Greylist: delayed 903 seconds by postgrey-1.27 at vger.kernel.org; Tue, 26 Mar 2019 19:37:16 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 hjarqo1mqukm 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 e789bcdb59c1483f872385df55e33941; 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.e789bcdb59c1483f872385df55e33941 X-Mandrill-User: md_31050260 Date: Tue, 26 Mar 2019 23:22:12 +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 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