After my machine hangs, I reboot it and than fsck_lfs crashed.
The following is backtrace.

I'll keep this partition untouched for some time.  If anybody need more
information for debugging, I can provide it.

NetBSD chen.chizhovka.net 4.0_RC5 NetBSD 4.0_RC5 (GENERIC) #1: Fri Dec  7 21:33:13 EET 2007  cheusov@chen.chizhovka.net:/srv/obj/sys/arch/i386/compile/GENERIC i386

#0  0x08057c9a in rfw_update_single (vp=0xbedc580, lbn=20, ndaddr=72981247, size=8192)
    at pass6.c:189
#1  0x08058de4 in account_indir (vp=0xbedc580, dp=0xb3fc000, ilbn=-12, daddr=72981407, 
    lvl=0) at pass6.c:365
#2  0x08059120 in account_block_changes (dp=0xb3fc000) at pass6.c:410
#3  0x080591a6 in readdress_inode (dp=0xb3fc000, daddr=72981416) at pass6.c:438
#4  0x0805b5cb in pass6 () at pass6.c:741
#5  0x080525c3 in checkfilesys (filesys=0x80667e0 "/dev/rwd1f", mntpt=0x0, auxdata=0, 
    child=0) at main.c:264
#6  0x080522c5 in main (argc=0, argv=0xbfbfe304) at main.c:147

-- 
Best regards, Aleksey Cheusov.