Re: Notifier chains are unsafe

[Chandra Seetharaman]

On Wed, 2005-10-26 at 01:43 +0200, Andi Kleen wrote:
> Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> writes:
> 
> > Has anyone been bothered by the fact that notifier chains are not safe 
> > with regard to registration and unregistration while the chain is in use?
> > The notifier_chain_register and notifier_chain_unregister routines have 
> > writelock protections, but the corresponding readlock is never taken!
> 
> If you add locks to the reader make sure it is only taken
> if the list is non empty. Otherwise you will add unacceptable
> overhead to some fast paths.
>  
> Better would be likely to use RCU.

RCU will be a problem if the registered notifiers need to block.

> 
> -Andi
> -
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> 
-- 

----------------------------------------------------------------------
    Chandra Seetharaman               | Be careful what you choose....
              - sekharan@xxxxxxxxxx   |      .......you may get it.
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