Re: [Lse-tech] Subject: [RFC][PATCH] Fix for unsafe notifier chain mechanism

[Alan Stern <stern@rowland.harvard.edu>]

On Sat, 12 Nov 2005, Paul E. McKenney wrote:

> > > > > The above can simply be "n->next = *nl;".  The reason is that this change
> > > > > of state is not visible to RCU readers until after the following statement,
> > > > > and it therefore need not be an RCU-reader-safe assignment.  You only need
> > > > > to use rcu_assign_pointer() when the results of the assignment are
> > > > > immediately visible to RCU readers.
> > > > 
> > > > Correct, the rcu call isn't really needed.  It doesn't hurt perceptibly,
> > > > though, and part of the RCU documentation states:
> > > > 
> > > >  * ...  More importantly, this
> > > >  * call documents which pointers will be dereferenced by RCU read-side
> > > >  * code.
> > > > 
> > > > For that reason, I felt it was worth putting it in.
> > > 
> > > But the following statement does a much better job of documenting the
> > > pointer that is to be RCU-dereferenced.  Duplicate documentation can
> > > be just as confusing as no documentation.
> > 
> > It's not really duplicate documentation since _both_ pointers are to be 
> > RCU-dereferenced.  But maybe you mean that only the second pointer can be 
> > RCU-dereferenced at the time the write occurs?  I don't think that's what 
> > the documentation comment intended.
> 
> I am the guy who wrote that documentation ocmment.  ;-)

In that case I bow to your advice.  :-)

Alan Stern

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