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
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