10.1-STABLE one week old from svn - random hangs

[Wojciech Puchar]

i have a problem with FreeBSD-10.

To make it more probable one have to

1) reduce maxbcache. eg
kern.maxbcache=50000000

in loader.conf

but NOT doing this doesn't make problem disappear. it is just more rare.

2) use swap. But you don't need system that swaps heavily. Probably - it 
may not swap at all.

3) do lots of I/O

4) it is more often if you use virtualbox, but still - it is not required, 
just make problem more common.


The problem. At random moment system I/O stops. If you are running top at 
this moment, there are lots of prosesses stalled in vnread or biord. 
network keeps running, processes that doesn't need I/O still runs.

top often reports at least 10MB free memory.

seems like a deadlock. Anyone know that problem. How to trace it down?