On Wed, Aug 12, 2009 at 09:01:35AM -0400, Gregory Haskins wrote: > I think I understand what your comment above meant: You don't need to > do synchronize_rcu() because you can flush the workqueue instead to > ensure that all readers have completed. Yes. > But if thats true, to me, the > rcu_dereference itself is gratuitous, Here's a thesis on what rcu_dereference does (besides documentation): reader does this A: sock = n->sock B: use *sock Say writer does this: C: newsock = allocate socket D: initialize(newsock) E: n->sock = newsock F: flush On Alpha, reads could be reordered. So, on smp, command A could get data from point F, and command B - from point D (uninitialized, from cache). IOW, you get fresh pointer but stale data. So we need to stick a barrier in there. > and that pointer is *not* actually > RCU protected (nor does it need to be). Heh, if readers are lockless and writer does init/update/sync, this to me spells rcu. -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
