Christoph Hellwig f5f3f959b7 xfs: skip delalloc COW blocks in xfs_reflink_end_cow
The iomap direct I/O code issues a single ->end_io call for the whole
I/O request, and if some of the extents cowered needed a COW operation
it will call xfs_reflink_end_cow over the whole range.

When we do AIO writes we drop the iolock after doing the initial setup,
but before the I/O completion.  Between dropping the lock and completing
the I/O we can have a racing buffered write create new delalloc COW fork
extents in the region covered by the outstanding direct I/O write, and
thus see delalloc COW fork extents in xfs_reflink_end_cow.  As
concurrent writes are fundamentally racy and no guarantees are given we
can simply skip those.

This can be easily reproduced with xfstests generic/208 in always_cow
mode.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
2018-09-29 13:49:58 +10:00
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