On Fri, Feb 24, 2006 at 11:44:23AM -0500, Alan Stern wrote:
> In that case you should be worried not about acquiring and releasing the
> rwsem at the beginning and end of blocking_notifier_call_chain; you should
> be worried about all the RCU serialization in the core
> notifier_call_chain routine.
RCU doesn't synchronize readers.
> The atomic chains are a different matter. The ones that don't run in NMI
> context could use an rw-spinlock for protection, allowing them also to
> avoid memory barriers while going through the list. The notifier chains
> that do run in NMI don't have this luxury. Fortunately I don't think
> there are very many of them.
A read lock is a memory barrier. That's why I'm opposed to using non-rcu
style locking for them.
-ben
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