On Tue, Jan 24, 2017 at 09:37:32AM +0100, Christoph Hellwig wrote: > On Wed, Dec 07, 2016 at 02:46:34PM -0500, Brian Foster wrote: > > Only for end_fsb... xfs_bmap_btalloc() calls xfs_bmap_extsize_align() > > with the alignment, which rounds out the start and end offsets. > > ... and corrupts data in the direct I/O case. > > The problem is that the down-alignment in xfs_bmap_extsize_align will > now create a real extent that spans before the extent that we have > to COW in this write_begin call. But the area before might have been > a hole before the dio write that had just before been filled with > an allocation in the data fork. And due to the direct I/O end_io > interface that only covers the range of the whole write we don't > know at that point where exactly the COW operation started and will > happily splice back our front pad into the data fork, replacing > the just written data with garbage. xfs/228 and sometimes generic/199 > reproduce this nicely. Is this reproducible on the current tree or only with this patch series? Also, shouldn't the end_io handler only remap the range of the write, regardless of whether the initial allocation ended up preallocating over holes or purely a shared range? Perhaps what you are saying here is that we have a single dio write that spans wider than a shared data fork extent..? In that case, we iterate the range in xfs_reflink_reserve_cow(). We'd skip the start of the range that is a hole in the data fork, but as you say, the xfs_bmapi_reserve_delalloc() call for the part of the I/O on the shared extent can widen the COW fork allocation to before the extent in the data fork, possibly to before the start of the I/O. (Thus we end up allocating COW blocks over the hole anyways...). >From there we are going to drop into iomap_dio_rw(), which looks like it's going to check the COW fork for blocks and if found, write to those blocks (as opposed to doing a data fork allocation). AFAICT, that means the extent size hint shouldn't be a problem. What am I missing? Brian > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
