[lwip-devel] [bug #25821] lwip_recvfrom failed to reset sock->rcvevent, communication lost sync totally

[Wim Dumon]

Follow-up Comment #2, bug #25821 (project lwip):

I have just noticed a similar thing. lwip_select() says that there is
something to read on a non-blocking socket, but when I do read data, the
lwip_recvfrom call blocks while reading from the mbox, waiting for the mutex
(I used the windows port for now). And that causes my program to deadlock...

I traced this back and it always happens on heavy traffic conditions (e.g.
opening many connections and transferring data over them), when the mbox is
full (breakpoint on return ERR_MEM in recv_tcp() in api_msg.c). RCVPLUS events
are received by the sockets layer, but there is no data (mbox is empty, but
the receive event counter isn't, and lwip_recvfrom performs a blocking read
from an empty buffer).

For now, I moved
  SYS_ARCH_INC(conn->recv_avail, len);
and
  API_EVENT(conn, NETCONN_EVT_RCVPLUS, len);
to just before the return ERR_OK, and the deadlock disappears. But is this
correct?

I haven't tested this for UDP, but there seems to be something similar going
on there (at the end of recv_udp).


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