NFS mount attempts hangs with btrfs on server side

Greetings.


I am observing a case whereby NFS mounting seems to hang. A tcpdump 
trace reveals that it retries forever RPC and exchanging NFS messages 
without giving any warning or error message about what's wrong. There is 
no firewall active, and the NFSserver (.1) has the client (.101) 
unconditionally allowed.

It's a simple
mount -t nfs 192.168.100.1:/B/home/jengelh /home/jengelh -o tcp,intr,soft

/B is a btrfs volume. Mounting an ext4 volume over NFS instead completes 
in a splitsecond.

Attached is the pcap file (->wireshark pretty display for deciphering).

It seems pretty much independent of the Linux kernel used; I can 
reproduce this in both 2.6.33-rc8 as well as 2.6.31.12.