2.5.2-pre1 dbench 32 hangs in vmstat "b" state

While running "dbench 32" on 2.5.2-pre1:

I noticed the test was taking much longer than usual,
and I could not do a new "login".  

vmstat 8 looked like this:

r  b  w   swpd   free   buff  cache  si  so    bi    bo   in    cs us  sy  id
0 34  1      0 222504  12248 736088   0   0     0     0  103    59 0   0 100
1 34  1      0 222504  12248 736088   0   0     0     0  100    56 0   0 100
0 34  1      0 222504  12248 736088   0   0     0     0  103    59 0   0 100

<sysrq Sync Umount> did not print their "done" messages.
The "b" and "w" columns when up though:

r  b  w   swpd   free   buff  cache  si  so    bi    bo   in    cs us  sy  id
0 37  3      0 222456 12280 736092   0   0     0     0  222   269   0   0 100

There was no Oops.
2.5.1-dj3 completed dbench normally.

Configs between the 2 kernels:
diff 2.5.2-pre1 2.5.1-dj3
> CONFIG_IP_NF_QUEUE=m

2.5.1-pre1[01] and 2.5.1-final did not exhibit this behavior.

Hardware:
1333 Athlon
1GB RAM

CONFIG_HIGHMEM4G=y
CONFIG_HIGHMEM=y
-- 
Randy Hron