On Sat, Dec 20, 2014 at 06:51:33AM +0000, Al Viro wrote: > On Mon, Dec 15, 2014 at 08:56:15AM -0800, Christoph Hellwig wrote: > > On Mon, Dec 15, 2014 at 05:27:05PM +0100, Jan Kara wrote: > > > On Sun 14-12-14 21:26:56, Omar Sandoval wrote: > > > > The generic write code locks i_mutex for a direct_IO. Swap-over-NFS > > > > doesn't grab the mutex because nfs_direct_IO doesn't expect i_mutex to > > > > be held, but most direct_IO implementations do. > > > I think you are speaking about direct IO writes only, aren't you? For DIO > > > reads we don't hold i_mutex AFAICS. And also for DIO writes we don't > > > necessarily hold i_mutex - see for example XFS which doesn't take i_mutex > > > for direct IO writes. It uses it's internal rwlock for this (see > > > xfs_file_dio_aio_write()). So I think this is just wrong. > > > > The problem is that the use of ->direct_IO by the swap code is a gross > > layering violation. ->direct_IO is a callback for the filesystem, and > > the swap code need to call ->read_iter instead of ->readpage and > > ->write_tier instead of ->direct_IO, and leave the locking to the > > filesystem. > > The thing is, ->read_iter() and ->write_iter() might decide to fall back to > buffered IO path. XFS is unusual in that respect - there O_DIRECT ends up > with short write in such case. Other filesystems, OTOH... Alright, now what? Using ->direct_IO directly is pretty much a no go because of the different locking conventions as was pointed out. Maybe some "no, really, just direct I/O" iocb flag? -- Omar -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>