On Mon, Nov 26, 2012 at 12:05:57PM -0800, Hugh Dickins wrote: > On Mon, 26 Nov 2012, Theodore Ts'o wrote: > > On Mon, Nov 26, 2012 at 04:33:28PM +0000, bugzilla-daemon@xxxxxxxxxxxxxxxxxxx wrote: > > > https://bugzilla.kernel.org/show_bug.cgi?id=50981 > > > > > > as this is working properly with XFS, so in ext4/ext3...etc also we shouldn't > > > require synchronization at the Application level,., FS should take care of > > > locking... will we expecting the fix for the same ??? > > > > Meetmehiro, > > > > At this point, there seems to be consensus that the kernel should take > > care of the locking, and that this is not something that needs be a > > worry for the application. > > Gosh, that's a very sudden new consensus. The consensus over the past > ten or twenty years has been that the Linux kernel enforce locking for > consistent atomic writes, but skip that overhead on reads - hasn't it? I was wondering exactly the same thing. > > So the question is whether every file system which supports AIO should > > add its own locking, or whether it should be done at the mm layer, and > > at which point the lock in the XFS layer could be removed as no longer > > necessary. (This has nothing to do with AIO. Buffered reads have been copied from unlocked pages.. basically forever, right?) > Thanks, that's helpful; but I think linux-mm people would want to defer > to linux-fsdevel maintainers on this: mm/filemap.c happens to be in mm/, > but a fundamental change to VFS locking philosophy is not mm's call. > > I don't see that page locking would have anything to do with it: if we > are going to start guaranteeing reads atomic against concurrent writes, > then surely it's the size requested by the user to be guaranteed, > spanning however many pages and fs-blocks: i_mutex, or a more > efficiently crafted alternative. Agreed. While this little racing test might be fixed, those baked in page_size == 4k == atomic granularity assumptions are pretty sketchy. So we're talking about holding multiple page locks? Or i_mutex? Or some fancy range locking? There's consensus on serializing overlapping buffered reads and writes? - z *readying the read(, mmap(), ) fault deadlock toy* -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
