From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:43910 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754213AbdASTAN (ORCPT ); Thu, 19 Jan 2017 14:00:13 -0500 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 619EE85545 for ; Thu, 19 Jan 2017 19:00:14 +0000 (UTC) Received: from bfoster.bfoster (dhcp-41-20.bos.redhat.com [10.18.41.20]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id v0JJ0EEp014673 for ; Thu, 19 Jan 2017 14:00:14 -0500 From: Brian Foster Subject: [PATCH v2 3/3] xfs: fix eofblocks race with file extending async dio writes Date: Thu, 19 Jan 2017 14:00:11 -0500 Message-Id: <1484852411-1137-4-git-send-email-bfoster@redhat.com> In-Reply-To: <1484852411-1137-1-git-send-email-bfoster@redhat.com> References: <1484852411-1137-1-git-send-email-bfoster@redhat.com> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: linux-xfs@vger.kernel.org It's possible for post-eof blocks to end up being used for direct I/O writes. dio write performs an upfront unwritten extent allocation, sends the dio and then updates the inode size (if necessary) on write completion. If a file release occurs while a file extending dio write is in flight, it is possible to mistake the post-eof blocks for speculative preallocation and incorrectly truncate them from the inode. This means that the resulting dio write completion can discover a hole and allocate new blocks rather than perform unwritten extent conversion. This requires a strange mix of I/O and is thus not likely to reproduce in real world workloads. It is intermittently reproduced by generic/299. The error manifests as an assert failure due to transaction overrun because the aforementioned write completion transaction has only reserved enough blocks for btree operations: XFS: Assertion failed: tp->t_blk_res_used <= tp->t_blk_res, \ file: fs/xfs//xfs_trans.c, line: 309 The root cause is that xfs_free_eofblocks() uses i_size to truncate post-eof blocks from the inode, but async, file extending direct writes do not update i_size until write completion, long after inode locks are dropped. Therefore, xfs_free_eofblocks() effectively truncates the inode to the incorrect size. Update xfs_free_eofblocks() to serialize against dio similar to how extending writes are serialized against i_size updates before post-eof block zeroing. Specifically, wait on dio while under the iolock. This ensures that dio write completions have updated i_size before post-eof blocks are processed. Signed-off-by: Brian Foster --- fs/xfs/xfs_bmap_util.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c index 81fac29..8170e30 100644 --- a/fs/xfs/xfs_bmap_util.c +++ b/fs/xfs/xfs_bmap_util.c @@ -951,6 +951,9 @@ xfs_free_eofblocks( if (error) return error; + /* wait on dio to ensure i_size has settled */ + inode_dio_wait(VFS_I(ip)); + error = xfs_trans_alloc(mp, &M_RES(mp)->tr_itruncate, 0, 0, 0, &tp); if (error) { -- 2.7.4