On Sat, Jul 01, 2017 at 12:03:06AM -0700, Darrick J. Wong wrote: > On Fri, Jun 30, 2017 at 07:37:40PM +0200, Christoph Hellwig wrote: > > On Fri, Jun 30, 2017 at 01:51:10PM +0200, Andreas Gruenbacher wrote: > > > Also, ext4 no longer calls inode_lock or inode_lock_shared; that needs > > > to be added back for consistency between reading i_size and walking > > > the file extents. > > > > At least for XFS we never had such a consistency as we never took > > the iolock (aka i_rwsem). > > Do we need it? For XFS I'm pretty sure we don't. The lseek is fundamentally safe without it due to the ilock. > The non-ext4 mechanical parts look ok to me (and test out ok), but I > want to be sure that we don't create a locking mess. Dave complained in > an earlier thread about lockdep problems because the old code took the > ilock and then started locking pages; since we take the ILOCK > during ->iomap_begin, drop it, and only take page locks during > page_cache_seek_hole_data (which is called from the iomap actor) I think > that particular problem goes away. The old code took the ilook in the seek hole/data helper, which had two problems: it double locked the ilock as we take it in iomap, and it hols the ilock over the page cache calls. None of which happen with this code.
