Hi Andrei,
On Mon, Jan 30, 2012 at 10:45 AM, Emeltchenko Andrei
<Andrei.Emeltchenko.news@xxxxxxxxx> wrote:
> On Mon, Jan 30, 2012 at 10:14:15AM -0200, Ulisses Furquim wrote:
>> On Mon, Jan 30, 2012 at 8:07 AM, Emeltchenko Andrei
>> <Andrei.Emeltchenko.news@xxxxxxxxx> wrote:
>> > On Fri, Jan 27, 2012 at 07:30:27PM -0200, Ulisses Furquim wrote:
>> >> On Fri, Jan 27, 2012 at 12:24 PM, Emeltchenko Andrei
>> >> <Andrei.Emeltchenko.news@xxxxxxxxx> wrote:
>> >> > /* ---- L2CAP connections ---- */
>> >> > @@ -747,15 +777,13 @@ static void l2cap_conn_start(struct l2cap_conn *conn)
>> >> >
>> >> > BT_DBG("conn %p", conn);
>> >> >
>> >> > - rcu_read_lock();
>> >> > -
>> >> > - list_for_each_entry_rcu(chan, &conn->chan_l, list) {
>> >> > + list_for_each_entry(chan, &conn->chan_l, list) {
>> >> > struct sock *sk = chan->sk;
>> >> >
>> >> > - bh_lock_sock(sk);
>> >> > + l2cap_chan_lock(chan);
>> >> >
>> >> > if (chan->chan_type != L2CAP_CHAN_CONN_ORIENTED) {
>> >> > - bh_unlock_sock(sk);
>> >> > + l2cap_chan_unlock(chan);
>> >> > continue;
>> >> > }
>> >> >
>> >> > @@ -764,7 +792,7 @@ static void l2cap_conn_start(struct l2cap_conn *conn)
>> >> >
>> >> > if (!l2cap_chan_check_security(chan) ||
>> >> > !__l2cap_no_conn_pending(chan)) {
>> >> > - bh_unlock_sock(sk);
>> >> > + l2cap_chan_unlock(chan);
>> >> > continue;
>> >> > }
>> >> >
>> >> > @@ -774,7 +802,7 @@ static void l2cap_conn_start(struct l2cap_conn *conn)
>> >> > /* l2cap_chan_close() calls list_del(chan)
>> >> > * so release the lock */
>> >> > l2cap_chan_close(chan, ECONNRESET);
>> >> > - bh_unlock_sock(sk);
>> >> > + l2cap_chan_unlock(chan);
>> >> > continue;
>> >> > }
>> >> >
>> >> > @@ -794,6 +822,7 @@ static void l2cap_conn_start(struct l2cap_conn *conn)
>> >> > rsp.dcid = cpu_to_le16(chan->scid);
>> >> >
>> >> > if (l2cap_chan_check_security(chan)) {
>> >> > + lock_sock(sk);
>> >> > if (bt_sk(sk)->defer_setup) {
>> >> > struct sock *parent = bt_sk(sk)->parent;
>> >> > rsp.result = cpu_to_le16(L2CAP_CR_PEND);
>> >> > @@ -802,10 +831,11 @@ static void l2cap_conn_start(struct l2cap_conn *conn)
>> >> > parent->sk_data_ready(parent, 0);
>> >> >
>> >> > } else {
>> >> > - l2cap_state_change(chan, BT_CONFIG);
>> >> > + __l2cap_state_change(chan, BT_CONFIG);
>> >> > rsp.result = cpu_to_le16(L2CAP_CR_SUCCESS);
>> >> > rsp.status = cpu_to_le16(L2CAP_CS_NO_INFO);
>> >> > }
>> >> > + release_sock(sk);
>> >> > } else {
>> >> > rsp.result = cpu_to_le16(L2CAP_CR_PEND);
>> >> > rsp.status = cpu_to_le16(L2CAP_CS_AUTHEN_PEND);
>> >> > @@ -816,7 +846,7 @@ static void l2cap_conn_start(struct l2cap_conn *conn)
>> >> >
>> >> > if (test_bit(CONF_REQ_SENT, &chan->conf_state) ||
>> >> > rsp.result != L2CAP_CR_SUCCESS) {
>> >> > - bh_unlock_sock(sk);
>> >> > + l2cap_chan_unlock(chan);
>> >> > continue;
>> >> > }
>> >> >
>> >> > @@ -826,10 +856,8 @@ static void l2cap_conn_start(struct l2cap_conn *conn)
>> >> > chan->num_conf_req++;
>> >> > }
>> >> >
>> >> > - bh_unlock_sock(sk);
>> >> > + l2cap_chan_unlock(chan);
>> >> > }
>> >> > -
>> >> > - rcu_read_unlock();
>> >> > }
>> >>
>> >> You are removing the RCU usage which was protecting conn->chan_l. What
>> >> are you going to use to protect this list? The RCU usage in the case
>> >> of conn->chan_l is missing a lock in the updaters of the list IMO,
>> >> though.
>> >
>> > I think that RCU usage is not correct here since we can delete element
>> > from the list and then take the reference, this shall be changed to
>> > list_for_each_entry_safe as it was originally.
>>
>> This is one of the reader sides of RCU for conn->chan_l so there's no
>
> I think that l2cap_chan_close deletes channel so this is not the reader.
I haven't checked if l2cap_chan_close rellay deletes channel but it
used to have a read_lock/read_unlock here which was converted to a
mutex and then to rcu_read_lock/rcu_read_unlock calls. If we are not
reader here then it's long time bug, I'm afraid.
>> need to use the _safe() version for list traversal. The write sides
>> you haven't touched with this patch. Moreover, there's no problem with
>> list RCU and removing elements, deleting more than one element needs
>> the _safe() version of list traversal using RCU or not.
>
> I think that freeing element needs the _safe version since list_del
> poisons next and prev pointers (with RCU case only prev is poisoned but in our
> code we give no chance by freeing also list element ;)).
Freeing elements only need _safe() version if you continue to iterate,
of course, and that's the case for RCU or not.
>> >> You are also changing bh_lock_sock which is a spin_lock to chan_lock
>> >> on a mutex and that might lead to issues. IIRC Padovan left
>> >> bh_lock_sock here so we don't sleep inside RCU reader section which
>> >> was causing deadlocks and long delays.
>> >
>> > I think that you cannot sleep in the RCU critical section in principle.
>> > bh_lock_sock looks like a hack to allow use RCU critical section but as I
>> > said above it looks completely wrong.
>>
>> Padovan wanted to revisit this sock spinlock usage later but it's
>> certainly not completely wrong. Send your proposal to revert it back
>> to chan_lock mutex and let's see what he says.
>
> I am thinking about using chan_lock mutex in updater side and when we have
> to sleep.
Best regards,
--
Ulisses Furquim
ProFUSION embedded systems
http://profusion.mobi
Mobile: +55 19 9250 0942
Skype: ulissesffs
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