On 05/22/2012 01:21 AM, Gustavo Padovan wrote:
> Hi Minho,
>
> * Minho Ban <mhban@xxxxxxxxxxx> [2012-05-21 09:56:40 +0900]:
>
>> l2cap_sock_kill can be called in l2cap_sock_release and l2cap_sock_close_cb
>> either. This lead l2cap_chan_destroy to be called twice for same channel.
>> To prevent double list_del and double chan_put, chan_destroy should be protected
>> with chan->refcnt and chan_list_lock so that reentrance could be forbidden.
>
> Even if l2cap_sock_kill() is called twice it will call l2cap_chan_destroy()
> only once. If this is not happening we just have a broken piece of code
> somewhere else and not here.
>
> Gustavo
>
Thanks for comment but I could not found any suitable code in l2cap_sock_kill that
can make l2cap_chan_destroy to be called just once. sock flag test is not enough to
do it.
I agree this path should not be the fix. Testing chan->refcnt is nonsense because
chan might have been freed already. So I looked for another point,
@@ -1343,10 +1343,10 @@ static void l2cap_conn_del(struct hci_conn *hcon, int err)
l2cap_chan_lock(chan);
l2cap_chan_del(chan, err);
+ chan->ops->close(chan->data);
l2cap_chan_unlock(chan);
- chan->ops->close(chan->data);
l2cap_chan_put(chan);
}
close callback must locate within chan_lock unless it can be scheduled to other thread
which may wait for chan_lock in l2cap_sock_shutdown and this lead to duplicate sock_kill.
static void l2cap_sock_kill(struct sock *sk)
{
- if (!sock_flag(sk, SOCK_ZAPPED) || sk->sk_socket)
+ if (!sock_flag(sk, SOCK_ZAPPED) || sock_flag(sk, SOCK_DEAD) ||
+ sk->sk_socket)
return;
BT_DBG("sk %p state %s", sk, state_to_string(sk->sk_state));
Duplicate sock_kill may happen anyway, need test SOCK_DEAD if chan_destroy is already called.
Regards,
Minho Ban
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