Messages in this thread | | | Date | Fri, 24 Feb 2006 11:44:15 -0500 | From | Benjamin LaHaise <> | Subject | Re: [PATCH] Avoid calling down_read and down_write during startup |
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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.
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