em regression, UDP LOR followed by ssh stall

[Harald Schmalzbauer]

Hello,

with RELENG_8 from 6 weeks ago I never ran into the problem that my ssh 
connection stalled.
With today's RELENG_8 it reproducably hangs at first login. After some 
time I can open another ssh session which seems to stay without 
problems, but the first sessions is always dying a few seconds after login.
here's a LOR:

lock order reversal:
  1st 0xffffff0001801018 em0:rx(1) (em0:rx(1)) @ 
/usr/src/sys/dev/e1000/if_em.c:4057
  2nd 0xffffffff80938908 udp (udp) @ /usr/src/sys/netinet/udp_usrreq.c:474
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2a
_witness_debugger() at _witness_debugger+0x49
witness_checkorder() at witness_checkorder+0x7ea
_rw_rlock() at _rw_rlock+0x58
udp_input() at udp_input+0x1cd
ip_input() at ip_input+0xb3
netisr_dispatch_src() at netisr_dispatch_src+0x9e
ether_demux() at ether_demux+0x176
ether_input() at ether_input+0x176
em_rxeof() at em_rxeof+0x175
em_msix_rx() at em_msix_rx+0x22
intr_event_execute_handlers() at intr_event_execute_handlers+0x67
ithread_loop() at ithread_loop+0xae
fork_exit() at fork_exit+0x12a
fork_trampoline() at fork_trampoline+0xe
--- trap 0, rip = 0, rsp = 0xffffff8075507d30, rbp = 0 ---

FreeBSD 8.0-STABLE #0: Fri Apr 16 10:34:36 CEST 2010 
admin at korso.rzhp.omnilan.net:/usr/obj/usr/src/sys/ILZ-S32  amd64

em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
options=399b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,TSO4,WOL_UCAST,WOL_MCAST,WOL_MAGIC>
	ether 00:1b:21:3e:90:52
	inet 10.21.0.2 netmask 0xffffff00 broadcast 10.21.0.255
	media: Ethernet autoselect (1000baseT <full-duplex>)
	status: active

em0: <Intel(R) PRO/1000 Network Connection 7.0.0> port 0x2000-0x201f mem 
0xe1a80000-0xe1a9ffff,0xe1a00000-0xe1a7ffff,0xe1aa0000-0xe1aa3fff irq 16 
at device 0.0 on pci1
em0: Using MSIX interrupts with 5 vectors
em0: [ITHREAD]
em0: [ITHREAD]
em0: [ITHREAD]
em0: [ITHREAD]
em0: [ITHREAD]
em0: Ethernet address: 00:1b:21:3e:90:52


Thanks for any help

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