Re: [PATCH] radix-tree: cleanup radix_tree_deref_slot() and _lookup_slot() comments

[Lee Schermerhorn <Lee.Schermerhorn@hp.com>]

On Wed, 2006-08-23 at 22:24 -0700, Paul E. McKenney wrote:
> On Tue, Aug 22, 2006 at 04:32:52PM -0400, Lee Schermerhorn wrote:
> > Andrew:  here is a second patch that just cleans up [I think] the
> > '_deref_slot() function, and adds more explanation of expected/required
> > locking to the direct slot access functions.  I separated it out,
> > because it doesn't fix a serious bug, like the previous one.
> > 
> > Paul:  do you agree that we don't need rcu_dereference() in the
> > _deref_slot() as it can only be used while the tree is held [probably
> > write] locked?  Do the comments look OK?
> 
> Yep, rcu_dereference() is not needed if the tree is prevented from
> changing.  That said, rcu_dereference() is zero cost on all but
> Alpha, so there is little benefit to be had from removing it.

I wasn't concerned about the cost.  I just thought it would be
"misleading" if, as you have verified, that it's not required, because
the comment on rcu_dereference() says that one important aspect of using
rcu_dereference() is to document which pointers are protected by RCU.  

> 
> The comments look much improved.

Thanks,
Lee

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