This is a note to let you know that I've just added the patch titled
xfs: fix eofblocks race with file extending async dio writes
to the 4.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
xfs-fix-eofblocks-race-with-file-extending-async-dio-writes.patch
and it can be found in the queue-4.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From e4229d6b0bc9280f29624faf170cf76a9f1ca60e Mon Sep 17 00:00:00 2001
From: Brian Foster <bfoster@xxxxxxxxxx>
Date: Fri, 27 Jan 2017 23:22:57 -0800
Subject: xfs: fix eofblocks race with file extending async dio writes
From: Brian Foster <bfoster@xxxxxxxxxx>
commit e4229d6b0bc9280f29624faf170cf76a9f1ca60e upstream.
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@xxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/xfs/xfs_bmap_util.c | 3 +++
1 file changed, 3 insertions(+)
--- 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) {
Patches currently in stable-queue which might be from bfoster@xxxxxxxxxx are
queue-4.10/xfs-use-iomap-new-flag-for-newly-allocated-delalloc-blocks.patch
queue-4.10/xfs-handle-indlen-shortage-on-delalloc-extent-merge.patch
queue-4.10/xfs-reject-all-unaligned-direct-writes-to-reflinked-files.patch
queue-4.10/xfs-don-t-fail-xfs_extent_busy-allocation.patch
queue-4.10/xfs-sync-eofblocks-scans-under-iolock-are-livelock-prone.patch
queue-4.10/xfs-pull-up-iolock-from-xfs_free_eofblocks.patch
queue-4.10/xfs-split-indlen-reservations-fairly-when-under-reserved.patch
queue-4.10/xfs-fix-eofblocks-race-with-file-extending-async-dio-writes.patch
queue-4.10/xfs-fix-uninitialized-variable-in-_reflink_convert_cow.patch
queue-4.10/xfs-don-t-reserve-blocks-for-right-shift-transactions.patch