5.1.2 hangs up

[Aleksey Cheusov <cheusov%tut.by@localhost>]

My NetBSD-5.1.2 box hangs up very often when I run pkgsrc bulk
builds (twice a day or so).

It looks like a file system problem because keyboard seems to work, I'm
able to run new terminals, X applications such as xosview and
tkabber continue to work, I'm able to switch to a console
by typing C-M-Fn.

The problem is accessing the file system.
For example, "ls -la /srv" stalls (/srv is a mount point),
ls process cannot be killed by sending SIGINT, SIGTERM and other
signals.

"ktrace + kdump" output ends like the following

 17669      1 ls       CALL  __lstat30(0x7f7ffd8031b8,0x7f7ffd8031c0)
 17669      1 ls       NAMI  "/srv"

I don't think the problem came with 5.1.2, it "worked" the same
way with 5.1 too. SMART's long test says that HDD is fine.

Ideas?

-- 
Best regards, Aleksey Cheusov.