On 11/15/2015 01:32 PM, Rainer Weikusat wrote:
>
> That was my original idea. The problem with this is that the code
> starting after the _lock and running until the main code path unlock has
> to be executed in one go with the other lock held as the results of the
> tests above this one may become invalid as soon as the other lock is
> released. This means instead of continuing execution with the send code
> proper after the block in case other became receive-ready between the
> first and the second test (possible because _dgram_recvmsg does not
> take the unix state lock), the whole procedure starting with acquiring
> the other lock would need to be restarted. Given sufficiently unfavorable
> circumstances, this could even turn into an endless loop which couldn't
> be interrupted. (unless code for this was added).
>
hmmm - I think we can avoid it by doing the wakeup from the write path
in the rare case that the queue has emptied - and avoid the double lock. IE:
unix_state_unlock(other);
unix_state_lock(sk);
err = -EAGAIN;
if (unix_peer(sk) == other) {
unix_dgram_peer_wake_connect(sk, other);
if (skb_queue_len(&other->sk_receive_queue) == 0)
need_wakeup = true;
}
unix_state_unlock(sk);
if (need_wakeup)
wake_up_interruptible_poll(sk_sleep(sk), POLLOUT
| POLLWRNORM | POLLWRBAND);
goto out_free;
Thanks,
-Jason
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