dump is stuck

hi,
	while running 'dump 0f - /dist | restore rf -'
the dump proc. got stuck, it seems it's waiting on some lock:

UID   PID  PPID CPU PRI NI   VSZ  RSS MWCHAN STAT  TT       TIME COMMAND

 0 30924 30922   0   4  0  3396 2852 sbwait T     p1    1:00.88 dump: 
/dev/amrd0s3h: ...
 0 30925 30924   1  -8  0  3268 2784 physrd TL    p1    0:53.84 dump 0f - 
/dist (dump)
 0 30926 30924   1  20  0  3268 2784 pause  T     p1    0:53.69 dump 0f - 
/dist (dump)
 0 30927 30924   1  20  0  3268 2784 pause  T     p1    0:54.12 dump 0f - 
/dist (dump)

(this is  5.3-STABLE, cvs'ed about a week ago, and it's a SMP system).
how can i find which lock? or who is holding it?

thanks,
	danny