occational system lock up in 6.0_BETA and 6.99.5

Hi,

I need a help from powerpc kernel knowledgefuls.  My sandpoint
NAS is known to make system lock ups under certain heavy
loads.

1. dump(8) or fsck_ffs(8) with -X/-x filesys snapshot. WAPBL enabled.
2. doing powerpc GCC4.5 compilation for genautomata

Right this moment I got another lockup symptom.  I found it
is capable to respond DDB break in.

- KUROBOX 64MB RAM plus 512MB swap space.
- it has continued "build.sh tools" for 7h18m.
- system is under severe VM slashing condition. For most of
time the offending compile process makes continuous page
out/in operation.

$ top
31 processes: 30 sleeping, 1 on CPU
CPU states:  0.0% user,  0.0% nice,  0.0% system,  0.0% interrupt,  100% idle
Memory: 29M Act, 15M Inact, 4K Wired, 2612K Exec, 6568K File, 464K Free
Swap: 512M Total, 455M Used, 57M Free

  PID USERNAME PRI NICE   SIZE   RES STATE      TIME   WCPU    CPU COMMAND
11089 nisimura  85    0   439M   35M biowait   38:49  0.00%  0.00% genautomata
    0 root     221    0     0K 4972K pgdaemon   8:20  0.00%  0.00% [system]
29191 nisimura  43    0  4316K 1572K CPU        0:38  0.00%  0.00% top
  817 root      85    0  8432K  452K select     0:35  0.00%  0.00% telnetd
10498 nisimura  85    0    12M  364K wait       0:09  0.00%  0.00% nbgmake
  452 root      85    0  3832K  440K biowait    0:02  0.00%  0.00% cron
... genautomata shows biowait for most of time with little occurrence of RUN.

$ /store/bin/build-sandpoint tools
^C^C^C ..... serial console echoes back ^C but gets no go.
~# ... sending BREAK does work.
Stopped in pid 0.2 (system) at  netbsd:cpu_Debugger+0x10:       lwz     r0, 0x14(r1)
db> bt
0x0060bd90: at comintr+0x590
0x0060bde0: at pic_handle_intr+0x198
0x0060be20: at trapstart+0x684
0x0060bef0: at sched_curcpu_runnable_p+0x2c
0x0060bf00: at idle_loop+0xe8
0x0060bf20: at cpu_lwp_bootstrap+0xc
saved LR(0x7ffffd) is invalid.
db> ps
PID    LID S CPU     FLAGS       STRUCT LWP *               NAME WAIT
29191    1 3   0         0            1c2a460                top biowait
11089    1 3   0   1000000            1c2aca0        genautomata biowait
18064    1 3   0   1000000            1c2a9e0                 sh biowait
10498    1 3   0   1000000            1fdf700            nbgmake biowait
1609     1 3   0   1000000            32b3c20                 sh biowait
15661    1 3   0   1000000            1fdf440            nbgmake biowait
28200    1 3   0   1000000            2426420                 sh biowait
25248    1 3   0   1000000            32b33e0             nbmake biowait
11259    1 3   0   1000000            30f2140                 sh biowait
24980    1 3   0   1000000            24269a0             nbmake biowait
26629    1 3   0   1000000            30f2400                 sh biowait
... not particularly useful information, I think.

Can someone get any clue from the above inspection? 

Toru Nishimura / ALKYL Technology