Possible race condition in RP2040 library

[glenn-dickins]

@GiungKim
Hey, I am using this library and going hard with the W5500 on RP2040.
I am doing some heavy traffic - about 25MBps of audio and HTTP.

I think I found a race condition - took me a while to trace it through, but I found sockets falling out of use, and the code was locking somewhere. I am load testing with about 200-300 HTTP connects/s.

Line 248 of socket.c in the listen function.
The state may have already progressed to SOCK_ESTABLISED

index 412a65d..0239e84 100644
--- a/Ethernet/socket.c
+++ b/Ethernet/socket.c
@@ -245,7 +245,7 @@ int8_t listen(uint8_t sn)
CHECK_SOCKINIT();
setSn_CR(sn,Sn_CR_LISTEN);
while(getSn_CR(sn));

• while(getSn_SR(sn) != SOCK_LISTEN)

• while(getSn_SR(sn) != SOCK_LISTEN && getSn_SR(sn) != SOCK_ESTABLISHED) // May have already picked up a connection
  {
  close(sn);
  return SOCKERR_SOCKCLOSED;

This helps a bit, though I am still chasing another lock condition.