As a datapoint, for me, doing large file transfers from a server using
the recently imported nfe(4) driver, leads to a hang.

The network processes are stuck in kvakmem wait state. So are things
like login.

Around the time of the hang, and one more since, the console shows:

arp_drain: locked; punting

I'd hazzard a guess that there's an mbuf leak in nfe(4), though I don't
have KMEMSTATS enabled in this kernel to check yet.

-- 
David Maxwell, david@vex.net|david@maxwell.net --> Mastery of UNIX, like
mastery of language, offers real freedom. The price of freedom is always dear,
but there's no substitute. Personally, I'd rather pay for my freedom than live
in a bitmapped, pop-up-happy dungeon like NT. - Thomas Scoville