Hisashi T Fujinaka <htodd@twofifty.com> typed:
: I have a hard time reliably reproducing the error, though it occurs more
: than once a day. After a panic the system isn't completely locked up so
: I can get a stack trace, but I haven't figured out how to save it. The
: only thing I remember from the stack trace is soo_close.

My three variants (sorry, don't have kernel dates for them):

panic: m_copydata: m == 0, len 1
Begin traceback...
m_copydata(0,0,1,c1746278,c1584c40) at netbsd:m_copydata+0x81
tcp_build_datapkt(c158f480,c158d1c0,a47,1,34) at netbsd:tcp_build_datapkt+0x229
tcp_output(c158f480,4,0,0,0) at netbsd:tcp_output+0xcdb
tcp_disconnect(c158f480,0,c1584c70,c158d1c0,c1b1c300) at netbsd:tcp_disconnect+0x5c
tcp_usrreq(c158d1c0,6,0,0,0) at netbsd:tcp_usrreq+0x2a8
sodisconnect(c158d1c0,0,0,0,c158f480) at netbsd:sodisconnect+0x53
soclose(c158d1c0,7,0,0,c0309700) at netbsd:soclose+0x172
soo_close(cc97df58,ccaa3b2c,ccac7f3c,c01f7a93,cca2a5b4) at netbsd:soo_close+0x29
closef(cc97df58,ccaa3b2c,ccac7f5c,0,2) at netbsd:closef+0xce
syscall_plain() at netbsd:syscall_plain+0x7e

------------------------------------------------------------

panic: m_copydata: m == 0, len 1
Begin traceback...
m_copydata(0,0,1,c146bf78,c1473afc) at netbsd:m_copydata+0x81
tcp_build_datapkt(c1b32c08,c147ccb8,0,1,34) at netbsd:tcp_build_datapkt+0x229
tcp_output(c1b32c08,caf7b824,0,0,1) at netbsd:tcp_output+0xcdb
tcp_input(c1ab1600,14,6,c16dfe08,c1ab1600) at netbsd:tcp_input+0x1537
ip_input(c1ab1600,0,0,200246,0) at netbsd:ip_input+0x53f
ipintr(15001f,bfbf001f,1f,bfbf001f,83cdd20) at netbsd:ipintr+0x76
DDB lost frame for netbsd:Xsoftnet+0x41, trying 0xcc467fa8
Xsoftnet() at netbsd:Xsoftnet+0x41
--- interrupt ---
0x200206:
[...]
------------------------------------------------------------

panic: m_copydata: m == 0, len 1
Begin traceback...
m_copydata(0,0,1,c143897c,c1472d18) at netbsd:m_copydata+0x81
tcp_build_datapkt(c1ba48fc,c147c1c0,65a,1,34) at netbsd:tcp_build_datapkt+0x229
tcp_output(c1ba48fc,cc467e10,c16df208,caf1c824,c1ba48fc) at netbsd:tcp_output+0xd6b
tcp_sack_newack(c1ba48fc,caf1c824,cc467f08,caf1c838,1) at netbsd:tcp_sack_newack+0xed
tcp_input(c1462b00,14,6,c16dfe08,c1462b00) at netbsd:tcp_input+0x146a
ip_input(c1462b00,0,0,200246,0) at netbsd:ip_input+0x53f
ipintr(1f,bfbf001f,1f,bfbf001f,85ea2dc) at netbsd:ipintr+0x76
DDB lost frame for netbsd:Xsoftnet+0x41, trying 0xcc467fa8
Xsoftnet() at netbsd:Xsoftnet+0x41
--- interrupt ---
0x200202:
[...]