Re: [patch 1/3] radix tree: RCU lockless read-side

[Nick Piggin <nickpiggin@yahoo.com.au>]

Balbir Singh wrote:
> On 3/11/06, Nick Piggin <nickpiggin@yahoo.com.au> wrote:
>
> > Balbir Singh wrote:
> >
> > > <snip>
> > >
> > > >               if (slot->slots[i]) {
> > > > -                       results[nr_found++] = slot->slots[i];
> > > > +                       results[nr_found++] = &slot->slots[i];
> > > >                       if (nr_found == max_items)
> > > >                               goto out;
> > > >               }
> > >
> > >
> > > A quick clarification - Shouldn't accesses to slot->slots[i] above be
> > > protected using rcu_derefence()?
> >
> > I think we're safe here -- this is the _address_ of the pointer.
> > However, when dereferencing this address in _gang_lookup,
> > I think we do need rcu_dereference indeed.
>
>
> Yes, I saw the address operator, but we still derefence "slots" to get
> the address.

But we should have already rcu_dereference()ed "slot", right
(in the loop above this one)? That means we are now able to
dereference it, and the data at the other end will be valid.

--
SUSE Labs, Novell Inc.
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