nfsclient process stucks in nfsaio

[Rong-En Fan]

Hi,

After upgrading several our nfs clients from 5.4-RELEASE to 6.0-RELEASE
and some are now 6.1-PRERELEASE (a weeks ago). From time to time,
we saw some processes stuck in nfsaio, and unkillable. These processes
generate lots of traffic to nfs server (write to nfs, but nfs server's disk does
not really in write. from netstat, client sends ~100Mbps, on nfs server, iostat
does not show me ~12.5MB/s). The nfsd on the server side is either in RUN
or in ufs state. Server is running 5.5-PRELEASE as of yesterday.

Client mount options: rw,nosuid,bg,intr,nodev. Both client and server
are running
rpc.lockd, rpc.statd. I'm sure it's not related to any locking problems.

I have another set of nfs server/client both running 6.0-RELEASE. And I can
easily reproduce this situation on these two boxesnes, just by running

  dd if=/dev/zero of=/nfs/ooo bs=1m

If I do not add bs=1m, it works fine. Of all the boxes I mentioned above,
I did not do anything special to kernel config, i.e., they are GENERIC w/o
unnecessary devices and w/ firewal.  Basically, I can do anything on these
two boxes (they are not in production mode). Any suggestion are welcome.

Thanks,
Rong-En Fan