On Wed 23-01-13 00:00:17, Zheng Liu wrote: > On Tue, Jan 22, 2013 at 04:22:43PM +0100, Jan Kara wrote: > > On Tue 22-01-13 22:22:21, Zheng Liu wrote: > > > On Tue, Jan 22, 2013 at 02:44:00PM +0100, Jan Kara wrote: > > > > On Tue 22-01-13 15:11:24, Dmitry Monakhov wrote: > > > > > On Fri, 18 Jan 2013 13:00:37 +0100, Jan Kara <jack@xxxxxxx> wrote: > > > > > > When using indirect blocks there is no possibility to have any unwritten > > > > > > extents. So wait for them in ext4_ind_direct_IO() is just bogus. > > > > > But as soon as i remember indirect implementation may also be used by > > > > > extents based inodes 3074: ext4_ext_direct_IO > > > > > /* Use the old path for reads and writes beyond i_size. */ > > > > > if (rw != WRITE || final_size > inode->i_size) > > > > > return ext4_ind_direct_IO(rw, iocb, iov, offset, nr_segs); > > > > > > > > > > Am I missing ? > > > > Ah, that's a catch. Thanks for pointing that out! So my patch is wrong > > > > and that code path needs some cleaning and commenting. In particular I'm > > > > afraid using dioread_nolock for inodes with indirect map causes data > > > > exposure bugs when unlocked DIO read races with DIO write because such > > > > inodes don't support uninitialized extents. > > > > > > Sorry, but I am still confused. dioread_nolock is only for extent-based > > > file. So when a file system without extent feature, dioread_nolock > > > couldn't be enabled. It seems that we don't need to worry about > > > exposing stale data here. > > Well, you can have fs with extent feature enabled but still with inodes > > using indirect map. But as Dmitry pointed out, ext4_should_dioread_nolock() > > handles that correctly. So there's not a bug I was suspecting. > > Yep, the patch itself is fine. But that would be great if a comment is > added here. No, the patch is wrong. The code before the patch is correct. We can get to that code for extent based inode which has unwritten conversions pending and we need to wait for those as otherwise we could return 0s in places where we acknowledged successful write just a while ago. Or am I missing something? Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
