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

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Balbir Singh wrote:
On 3/11/06, Nick Piggin <[email protected]> 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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