LOR on em in HEAD ( was Re: em driver regression

While testing an i5 box with HEAD checked out from this morning, 
bringing up the second NIC generated this LOR on the console

em1: link state changed to UP
lock order reversal:
  1st 0xc5dc7c10 em1:rx(1) (em1:rx(1)) _at_ 
/usr/HEAD/src/sys/modules/em/../../dev/e1000/if_em.c:4089
  2nd 0xc0f7e88c udp (udp) _at_ /usr/HEAD/src/sys/netinet/udp_usrreq.c:454
KDB: stack backtrace:
db_trace_self_wrapper(c0cb4d33,c5b72a70,c08e4d65,c08d50db,c0cb7d58,...) 
at db_trace_self_wrapper+0x26
kdb_backtrace(c08d50db,c0cb7d58,c5d31a98,c5d2cb60,c5b72acc,...) at 
kdb_backtrace+0x29
_witness_debugger(c0cb7d58,c0f7e88c,c0c9cf0b,c5d2cb60,c0cd04ca,...) 
at _witness_debugger+0x25
witness_checkorder(c0f7e88c,1,c0cd04ca,1c6,0,...) at witness_checkorder+0x839
_rw_rlock(c0f7e88c,c0cd04ca,1c6,c5d33088,c5e8be24,...) at _rw_rlock+0x9c
udp_input(c67faa00,14,0,c5e8bd80,c0dfa860,...) at udp_input+0x246
ip_input(c67faa00,c5f2f380,c5b72be8,c07463b6,c0dfa860,...) at ip_input+0x606
netisr_dispatch_src(1,0,c67faa00,c5b72c20,c0954bc1,...) at 
netisr_dispatch_src+0xcd
netisr_dispatch(1,c67faa00,c6018c00,c6018c00,c6852800,...) at 
netisr_dispatch+0x20
ether_demux(c6018c00,c67faa00,3,0,3,...) at ether_demux+0x1a1
ether_input(c6018c00,c67faa00,c11a0e17,ff9,64,...) at ether_input+0x365
em_rxeof(c5e8bd80,109,c6016180,0,c5b72cc8,...) at em_rxeof+0x13c
em_msix_rx(c5dc7c00,c5b72cc8,c088eb14,c0e133c0,c60342b8,...) at em_msix_rx+0x25
intr_event_execute_handlers(c5d807f8,c6034280,c0cacd7e,533,c60342f0,...) 
at intr_event_execute_handlers+0x125
ithread_loop(c603b4a0,c5b72d38,c0cacaed,343,c5d807f8,...) at ithread_loop+0x9f
fork_exit(c0877800,c603b4a0,c5b72d38) at fork_exit+0xb8
fork_trampoline() at fork_trampoline+0x8
--- trap 0, eip = 0, esp = 0xc5b72d70, ebp = 0 ---

0(i5b)# uname -a
FreeBSD i5b.sentex.ca 9.0-CURRENT FreeBSD 9.0-CURRENT #2: Fri Apr  9 
11:56:25 EDT 
2010     mdtancsa_at_ich10.sentex.ca:/usr/HEAD/obj/usr/HEAD/src/sys/GENERIC  i386
0(i5b)#

em0_at_pci0:0:25:0:        class=0x020000 card=0x34ec8086 
chip=0x10ef8086 rev=0x05 hdr=0x00
     vendor     = 'Intel Corporation'
     class      = network
     subclass   = ethernet
     cap 01[c8] = powerspec 2  supports D0 D3  current D0
     cap 05[d0] = MSI supports 1 message, 64 bit enabled with 1 message
     cap 13[e0] = PCI Advanced Features: FLR TP
em1_at_pci0:3:0:0: class=0x020000 card=0x34ec8086 chip=0x10d38086 
rev=0x00 hdr=0x00
     vendor     = 'Intel Corporation'
     device     = 'Intel 82574L Gigabit Ethernet Controller (82574L)'
     class      = network
     subclass   = ethernet
     cap 01[c8] = powerspec 2  supports D0 D3  current D0
     cap 05[d0] = MSI supports 1 message, 64 bit
     cap 10[e0] = PCI-Express 1 endpoint max data 128(256) link x1(x1)
     cap 11[a0] = MSI-X supports 5 messages in map 0x1c enabled


0(i5b)#  vmstat -i
interrupt                          total       rate
irq4: uart0                         6156          3
irq8: rtc                         224879        127
irq21: ehci0                        2662          1
irq23: ehci1                        3674          2
cpu0: timer                      1754210        998
irq256: em0                        10778          6
irq257: em1                          331          0
irq258: em1                            4          0
irq260: em1                            4          0
irq261: em1                            8          0
irq262: ahci0                         69          0
cpu3: timer                      1753938        998
cpu2: timer                      1753932        998
cpu1: timer                      1753886        998
Total                            7264531       4134
0(i5b)#

CPU: Intel(R) Core(TM) i5 CPU         750  _at_ 2.67GHz (2666.65-MHz 
686-class CPU)
   Origin = "GenuineIntel"  Id = 0x106e5  Family = 6  Model = 1e  Stepping = 5
   Features=0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,DTS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE>
   Features2=0x98e3fd<SSE3,DTES64,MON,DS_CPL,VMX,SMX,EST,TM2,SSSE3,CX16,xTPR,PDCM,SSE4.1,SSE4.2,POPCNT>
   AMD Features=0x28100000<NX,RDTSCP,LM>
   AMD Features2=0x1<LAHF>
   TSC: P-state invariant
real memory  = 4294967296 (4096 MB)
avail memory = 2577711104 (2458 MB)
ACPI APIC Table: <INTEL  S3420GPC>
FreeBSD/SMP: Multiprocessor System Detected: 4 CPUs




--------------------------------------------------------------------
Mike Tancsa,                                      tel +1 519 651 3400
Sentex Communications,                            mike_at_sentex.net
Providing Internet since 1994                    www.sentex.net
Cambridge, Ontario Canada                         www.sentex.net/mike