Strange semi-hangs on 5.4

Hi all,

With relatively recent 5.4, I'm seeing hangs that worry me. The box  
(dual opteron) accepts keyboard input, but it won't actually DO  
anything.. SSHing in gives me a TCP session but no actualy password  
prompt. Trying to log in on (serial) console doesn't work, I just get  
a newline after entering the username, no password prompt. On SSH  
shells alredy open, I can't even get a new prompt line, all I get is  
newlines.

But the best part is: The kernel debugger doesn't seem to work. I've  
got BREAK_TO_DEBUGGER in my kernel config, but here's what happens:

telnet> send brk
KDB: enter: Line break on console
3KtDhB:a s tpaicdk  1b1a0e00:0
aitd l e _ p r o c ( )   a t   i d l e _ p r o c + 0 x 1 1 3
m???b >   o|?|??f?tpie  rat0f :          n o p
     dd
db>
db>
db
d
d
dd
db>
db
dd
db>
db
d
db>
dd

...and then it keeps spewing d's and db's and stuff at me at  
whichever speed my serial can handle. In other words, useless. All I  
can do at this point is log in to my power switch and powercycle the  
box.

Anyone?

/Eirik