On Tue 07-01-14 07:58:30, Christoph Hellwig wrote: > On Mon, Jan 06, 2014 at 09:10:32PM +0100, Jan Kara wrote: > > This is likely a problem of Linux direct IO implementation. The thing is > > that in Linux when you are doing appending direct IO (i.e., direct IO which > > changes file size), the IO is performed synchronously so that we have our > > life simpler with inode size update etc. (and frankly our current locking > > rules make inode size update on IO completion almost impossible). Since > > appending direct IO isn't very common, we seem to get away with this > > simplification just fine... > > Shouldn't be too much of a problem at least for XFS and maybe even ext4 > with the workqueue based I/O end handler. For XFS we protect size > updates by the ilock which we already taken in that handler, not sure > what ext4 would do there. Well, I was specifically worried about i_mutex locking. In particular: Before we report appending IO completion we need to update i_size. To update i_size we need to grab i_mutex. Now this is unpleasant because inode_dio_wait() happens under i_mutex so the above would create lock inversion. And we cannot really do inode_dio_done() before grabbing i_mutex as that would open interesting races between truncate decreasing i_size and DIO increasing it. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
