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authorBrian Foster <bfoster@redhat.com>2017-01-27 23:22:57 -0800
committerDarrick J. Wong <darrick.wong@oracle.com>2017-01-30 16:32:25 -0800
commite4229d6b0bc9280f29624faf170cf76a9f1ca60e (patch)
tree4be18297dc85e36e10004a27ca9094ca8917b38b /fs/xfs/xfs_bmap_util.c
parentc3155097ad89a956579bc305856a1f2878494e52 (diff)
downloadlinux-e4229d6b0bc9280f29624faf170cf76a9f1ca60e.tar.bz2
xfs: fix eofblocks race with file extending async dio writes
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 <bfoster@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Diffstat (limited to 'fs/xfs/xfs_bmap_util.c')
-rw-r--r--fs/xfs/xfs_bmap_util.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index 9319ee9759d4..eb890ed1ed5c 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -959,6 +959,9 @@ 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) {