[2.6.37] btrfs-transac hanging in prepare_to_wait

[Christian Schmidt <charlie@digadd.de>]

[-- Attachment #1: Type: text/plain, Size: 858 bytes --]

Hi,

After a few weeks of testing and preparation I commissioned a new NFS
server with btrfs for the main storage. I ran into two situations where
the btrfs locked up and I had to hard reboot the machine (sysrq-b).
I end up with btrfs-transac in state D, waiting for the pending
transaction to be completed if I interpret the code right. On top of
that all eight nfsds are in state D waiting to start several different
transactions.
I have attached the sysrq-t output after I killed all processes I could
before rebooting.

It only seems to happen with somewhat heavier IO load, in this case one
process md5summing large files (a few TB in total) while another process
tries to write to the NFS share. I never saw it e.g. while copying
single files onto the file system or reading multiple files.

I'll be glad for any hints and recommendations.

Christian


[-- Attachment #2: dmesg.bz2 --]
[-- Type: application/x-bzip2, Size: 15548 bytes --]