On Thu, Sep 20, 2018 at 04:42:17PM +0200, Christoph Hellwig wrote: > 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> Looks ok to me... Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> --D > --- > 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 >
