0

I am new to BSD TCP stack code here, but we have an application that converted and uses BSD TCP stack code in the user mode. I am debugging an issue that this application would hold (or not sending data) in a strange situation. I included part of the related callstack below.

Before calling sosend in uipc_socket, I have verified that the length stored in the top, _m0->m_pkthdr.len has the right value. The chain should hold 12 pieces of TCP payload each with 1368 bytes long. In the end, my callback function only got called 10 times instead of 12 and the 10 smaller mbuf chains contains less payload data after they were combined.

I checked each function in the call stack and I could not find a loop anywhere to iterate through from the head to the end of the mbuf chain as I expected. Only loops I could find was the nested do ... while() loops in sosend_generic of uipc_socket.c, however, my code path only executed the loop once, since the resid was set to 0 immediately after the (uio == NULL) check.

\#2  0x00007ffff1acb868 in ether_output_frame (ifp=0xbf5f290, m=0x7ffff7dfeb00) at .../freebsd_plebnet/net/if_ethersubr.c:457

\#3  0x00007ffff1acb7ef in ether_output (ifp=0xbf5f290, m=0x7ffff7dfeb00, dst=0x7fffffff2c8c, ro=0x7fffffff2c70) at .../freebsd_plebnet/net/if_ethersubr.c:429

\#4  0x00007ffff1ada20b in ip_output (m=0x7ffff7dfeb00, opt=0x0, ro=0x7fffffff2c70, flags=0, imo=0x0, inp=0x7fffd409e000) at .../freebsd_plebnet/netinet/ip_output.c:663
\#5  0x00007ffff1b0743b in tcp_output (tp=0x7fffd409c000) at /scratch/vindu/ec_intg/ims/src/third-party/nse/nsnet.git/freebsd_plebnet/netinet/tcp_output.c:1288

\#6  0x00007ffff1ae2789 in tcp_usr_send (so=0x7fffd40a0000, flags=0, m=0x7ffeda1b7270, nam=0x0, control=0x0, td=0x7ffff1d5f3d0) at .../freebsd_plebnet/netinet/tcp_usrreq.c:882

\#7  0x00007ffff1a93743 in sosend_generic (so=0x7fffd40a0000, addr=0x0, uio=0x0, top=0x7ffeda1b7270, control=0x0, flags=128, td=0x7ffff1d5f3d0) at .../freebsd_plebnet/kern/uipc_socket.c:1390

\#8  0x00007ffff1a9387d in sosend (so=0x7fffd40a0000, addr=0x0, uio=0x0, top=0x7ffeda1b7270, control=0x0, flags=128, td=0x7ffff1d5f3d0) at .../freebsd_plebnet/kern/uipc_socket.c:1434
user3894299
  • 15
  • 5
  • Perhaps a _tcpdump_ would give easier insight. And you should post a link to the used sources, as there are different versions. – Armali Aug 17 '16 at 06:59
  • 1
    Thanks, Armali. I realized the fact that our version of the BSD TCP stack code are quite old, after comparing to the current BSD stack code. I tracked down the root cause of the issue, basically it is related to the congestion window value in the TCP control block. – user3894299 Aug 18 '16 at 17:38

0 Answers0