I'm getting hundred of such messages in the kernel log with
2.4.20-rc1 and 2.4.20-rc1-ac2
Root is on nfs, and ide raid5 exported via nfs to the clients.
When any further details needed, let me know.
$ dmesg
RPC svc_write_space: some sleeping on dfae1ba0
RPC svc_write_space: some sleeping on dfae1ba0
RPC svc_write_space: some sleeping on dfae1ba0
[...]