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

    > Note that _gang_lookup_slot doesn't do this for us, however --
    > the caller must do that when dereferencing the pointer to the
    > item (eg. see page_cache_get_speculative in 2/3).

    Oh! I did not get that far. Will look at the rest of the series

    >
    > That said, I'm not 100% sure I have the rcu memory barriers in
    > the right places (well I'm sure I don't, given the _gang_lookup
    > bug you exposed!).

    Hmm... Let me look at rcu_torture module and see if I can figure it
    out or read the documentation again.

    >
    > Thanks,
    > Nick
    >

    Warm Regards,
    Balbir
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