Hello, On Fri 11-08-17 11:03:01, Lukas Czerner wrote: > On Thu, Aug 10, 2017 at 10:22:47AM -0400, Jeff Moyer wrote: > > Jan Kara <jack@xxxxxxx> writes: > > > > > On Thu 10-08-17 14:59:57, Lukas Czerner wrote: > > >> Currently when mixing buffered reads and asynchronous direct writes it > > >> is possible to end up with the situation where we have stale data in the > > >> page cache while the new data is already written to disk. This is > > >> permanent until the affected pages are flushed away. Despite the fact > > >> that mixing buffered and direct IO is ill-advised it does pose a thread > > >> for a data integrity, is unexpected and should be fixed. > > >> > > >> Fix this by deferring completion of asynchronous direct writes to a > > >> process context in the case that there are mapped pages to be found in > > >> the inode. Later before the completion in dio_complete() invalidate > > >> the pages in question. This ensures that after the completion the pages > > >> in the written area are either unmapped, or populated with up-to-date > > >> data. Also do the same for the iomap case which uses > > >> iomap_dio_complete() instead. > > >> > > >> This has a side effect of deferring the completion to a process context > > >> for every AIO DIO that happens on inode that has pages mapped. However > > >> since the consensus is that this is ill-advised practice the performance > > >> implication should not be a problem. > > >> > > >> This was based on proposal from Jeff Moyer, thanks! > > > > > > It seems the invalidation can be also removed from > > > generic_file_direct_write(), can't it? It is duplicit there the same way as > > > it was in the iomap code... > > > > Yep, sure looks that way. > > Hrm, ok. Technically speaking generic_file_direct_write does not have to > eventually end up with dio_complete() being called. This will change the > behaviour for those that implement dio differently. Looking at the users > now, vast majority will end up with complete_dio() so maybe this is not > a problem. OK, so this seems to be the problem with 9p, fuse, nfs, lustre. > This is in contrast with iomap_dio_rw() which will end up calling > iomap_dio_complete() so the situation is different there. > > Maybe adding mapping->nrpages check would be better than outright > removing it ? OK, I agree we cannot just remove the invalidation. But shouldn't we rather fix the above mentioned filesystems? Otherwise they will keep having issues you are trying to fix? But for now I could live with keeping the invalidation behind nrpages check and adding a comment why we kept it there... Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
