From patchwork Tue Jul 25 06:47:40 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nikolay Borisov X-Patchwork-Id: 9861265 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 50E47601A1 for ; Tue, 25 Jul 2017 06:47:46 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 3F7EF285FC for ; Tue, 25 Jul 2017 06:47:46 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 33BD3285FE; Tue, 25 Jul 2017 06:47:46 +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=-6.9 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, T_TVD_MIME_EPI 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 177F2285FC for ; Tue, 25 Jul 2017 06:47:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750794AbdGYGro (ORCPT ); Tue, 25 Jul 2017 02:47:44 -0400 Received: from mx2.suse.de ([195.135.220.15]:34265 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750793AbdGYGrn (ORCPT ); Tue, 25 Jul 2017 02:47:43 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 18AD8AB9D; Tue, 25 Jul 2017 06:47:42 +0000 (UTC) To: stable@vger.kernel.org Cc: linux-xfs@vger.kernel.org, Christoph Hellwig , Brian Foster , "Darrick J. Wong" From: Nikolay Borisov Subject: request for inclusion of 04197b341f23 ("xfs: don't BUG() on mixed direct and mapped I/O") Message-ID: <5bcfc94b-ecb9-468b-78f3-ae5de53f62a0@suse.com> Date: Tue, 25 Jul 2017 09:47:40 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 Content-Language: en-US Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Hello, I'd like to request the aforementioned patch to be included into stable kernels. I've attached the 4.4 backport, the patch got introduced in 4.10 so for 4.9 it will likely be able to apply cleanly, for 4.4 it needed a bit of adjustment. Regards, Nikolay Acked-by: Darrick J. Wong From: Brian Foster Date: Tue, 8 Nov 2016 12:54:14 +1100 Subject: xfs: don't BUG() on mixed direct and mapped I/O We've had reports of generic/095 causing XFS to BUG() in __xfs_get_blocks() due to the existence of delalloc blocks on a direct I/O read. generic/095 issues a mix of various types of I/O, including direct and memory mapped I/O to a single file. This is clearly not supported behavior and is known to lead to such problems. E.g., the lack of exclusion between the direct I/O and write fault paths means that a write fault can allocate delalloc blocks in a region of a file that was previously a hole after the direct read has attempted to flush/inval the file range, but before it actually reads the block mapping. In turn, the direct read discovers a delalloc extent and cannot proceed. While the appropriate solution here is to not mix direct and memory mapped I/O to the same regions of the same file, the current BUG_ON() behavior is probably overkill as it can crash the entire system. Instead, localize the failure to the I/O in question by returning an error for a direct I/O that cannot be handled safely due to delalloc blocks. Be careful to allow the case of a direct write to post-eof delalloc blocks. This can occur due to speculative preallocation and is safe as post-eof blocks are not accompanied by dirty pages in pagecache (conversely, preallocation within eof must have been zeroed, and thus dirtied, before the inode size could have been increased beyond said blocks). Finally, provide an additional warning if a direct I/O write occurs while the file is memory mapped. This may not catch all problematic scenarios, but provides a hint that some known-to-be-problematic I/O methods are in use. Signed-off-by: Brian Foster Reviewed-by: Dave Chinner Signed-off-by: Dave Chinner Signed-off-by: Nikolay Borisov --- fs/xfs/xfs_aops.c | 21 ++++++++++++++++++++- 1 file changed, 20 insertions(+), 1 deletion(-) diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c index d4752078b471..11fa73d8be78 100644 --- a/fs/xfs/xfs_aops.c +++ b/fs/xfs/xfs_aops.c @@ -1439,6 +1439,26 @@ __xfs_get_blocks( if (error) goto out_unlock; + /* + * The only time we can ever safely find delalloc blocks on direct I/O + * is a dio write to post-eof speculative preallocation. All other + * scenarios are indicative of a problem or misuse (such as mixing + * direct and mapped I/O). + * + * The file may be unmapped by the time we get here so we cannot + * reliably fail the I/O based on mapping. Instead, fail the I/O if this + * is a read or a write within eof. Otherwise, carry on but warn as a + * precuation if the file happens to be mapped. + */ + if (direct && imap.br_startblock == DELAYSTARTBLOCK) { + if (!create || offset < i_size_read(VFS_I(ip))) { + WARN_ON_ONCE(1); + error = -EIO; + goto out_unlock; + } + WARN_ON_ONCE(mapping_mapped(VFS_I(ip)->i_mapping)); + } + /* for DAX, we convert unwritten extents directly */ if (create && (!nimaps || @@ -1538,7 +1558,6 @@ __xfs_get_blocks( set_buffer_new(bh_result); if (imap.br_startblock == DELAYSTARTBLOCK) { - BUG_ON(direct); if (create) { set_buffer_uptodate(bh_result); set_buffer_mapped(bh_result); -- 2.7.4