panics/lock-ups while tcpdump-ing

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

I recently experienced a bunch of panics and lock-ups while tcpdump-ing on 
an 8.1/amd64 machine over ssh. The net I was tracing was different from the 
one the ssh connection was on.

1. panic: tp->tlastm == NULL (in sshd)
backtrace:
breakpoint
vpanic
snprintf
tcp_output
tcp_send_wrapper
sosend
soo_write
dofilewrite
sys_write
syscall

2. lock-up (in pid 0.3): wscons switching not working, numlock working, 
cursor flashes on keypresses. Could enter ddb:
backtrace (before interrupt)
sbappendadr
udp4_sendup
udp_input
ipintr
softint_dispatch
DDB lost frame
Xsoftintr

I could cont from there and re-enter ddb, giving the same backtrace.

3. panic: m_copym: m == 0, len 152 [!COPYALL] (in squid)
backtrace:
breakpoint
vpanic
snprintf
m_copym0
tcp_output
tcp_send_wrapper
sosend
soo_write
dofilewrite
sys_write
syscall


I do have show reg output of all three incidents.

Any clues?