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@xxxxxx> --- fs/xfs/xfs_reflink.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c index ac94ace45424..d1758771f21a 100644 --- a/fs/xfs/xfs_reflink.c +++ b/fs/xfs/xfs_reflink.c @@ -686,14 +686,12 @@ xfs_reflink_end_cow( if (!del.br_blockcount) goto prev_extent; - ASSERT(!isnullstartblock(got.br_startblock)); - /* - * Don't remap unwritten extents; these are - * speculatively preallocated CoW extents that have been - * allocated but have not yet been involved in a write. + * Only remap real extent that contain data. With AIO + * speculatively preallocations can leak into the range we + * are called upon, and we need to skip them. */ - if (got.br_state == XFS_EXT_UNWRITTEN) + if (!xfs_bmap_is_real_extent(&got)) goto prev_extent; /* Unmap the old blocks in the data fork. */ -- 2.18.0
