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

["Paul E. McKenney" <paulmck@us.ibm.com>]

On Thu, Aug 24, 2006 at 11:04:41AM -0400, Lee Schermerhorn wrote:
> 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.  

Fair enough!  My hope is that this will eventually be settled by
the needs of RCU-based static-analysis tooling, but we are not there
yet.

						Thanx, Paul

> > The comments look much improved.
> 
> Thanks,
> Lee
> 

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