Re: Notifier chains are unsafe

[Chandra Seetharaman <sekharan@us.ibm.com>]

On Wed, 2005-10-26 at 21:17 -0400, Joe Seigh wrote:
> Chandra Seetharaman wrote:
> > Andy, comment above rcu_read_lock says, "It is illegal to block while in
> > an RCU read-side critical section."
> > 
> > As i mentioned in the other email we are discussing about "task
> > notifier" in lse-tech. We thought of using RCU, but one of the
> > requirements was that the registered function should be able to block,
> > so we are looking for alternatives.
> > 
> 
> What are the requirements that preclude a conventional rwlock?  If you
> don't have any, then you should go with that.

I was thinking the problem is that we cannot hold any locks while
calling the callouts.

But, As Keith mentioned, we cannot even acquire a lock in the
notifier_call_chain.

Thanks,

chandra  
> 
> The other solutions I've mentioned before.
> 
> Copy on read.
> 
> Various lock-free schemes:
> SMR hazard pointers
> RCU+SMR (probably overkill since you don't need the read side performance)
> reference counting
> proxy reference counting
> 
> The last would probably be the easiest to implement expecially if you used
> a spinlock to safely increment the reference count without the more complicated
> atomic thread-safety.  It's also more self contained.
> 
> User land implementations of most of the above can be found at
> http://sourceforge.net/projects/atomic-ptr-plus/
> 
> The proxy refcounting stuff is in the atomic-ptr-plus package.  It's
> in c++ but you should be able to figure it out.
> 
> RCU+SMR is in the fastsmr package.
> 
> 
> 
> --
> Joe Seigh
> 
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-- 

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    Chandra Seetharaman               | Be careful what you choose....
              - sekharan@us.ibm.com   |      .......you may get it.
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