On Wed, Apr 07, 2010 at 09:34:38AM +1000, Dave Chinner wrote: > On Wed, Apr 07, 2010 at 03:09:03AM +1000, Nick Piggin wrote: > > On Tue, Apr 06, 2010 at 05:19:49PM +0100, David Howells wrote: > > > > > > Hi, > > > > > > I think I've made a bad assumption over my usage of radix_tree_tag_get() in > > > fs/fscache/page.c. > > > > > > I've assumed that radix_tree_tag_get() is protected from radix_tree_tag_set() > > > and radix_tree_tag_clear() by the RCU read lock. However, now I'm not so > > > sure. I think it's only protected against removal of part of the tree. > > > > > > Can you confirm? > > > > It is safe. Synchronization requirements for using the radix tree API > > are documented. > > I don't think it is safe - I made modifications to XFS that modified > radix tree tags under a read lock (not RCU), but this resulted in > corrupted tag state as concurrent tag set/clear operations for > different slots propagated through the tree and got mixed up. > Christoph fixed the problem (f1f724e4b523d444c5a598d74505aefa3d6844d2) > by putting all tag modifications under the write lock. I can't see > how doing tag modifications under RCU read locks is any safer than > doing it under a spinning read lock.... No the modifications must all be serialized, but they can run in parallel with a radix_tree_tag_get(). -- Linux-cachefs mailing list Linux-cachefs@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/linux-cachefs
