Hello!

Nfs4 client randomly hangs on a file or directory (for instance when 
performing df or find) and after a few seconds continues. When 
preforming strace, it hangs on getdents system call.

Errors on the server side:
Aug 19 21:29:08 host kernel: nfs: server host2 not responding, still trying
Aug 19 21:31:17 host kernel: nfs: server host2 OK

After a while the load on client and server side increases intensively, 
then system on the client side crashes. Reboot required.

We use SL6.3, the same problem occurred on the following kernels:
2.6.32-220.17.1.el6.x86_64
2.6.32-279.2.1.el6.x86_64

and also on:

3.5.2-1.el6.elrepo.x86_64
3.3.2-1.el6.elrepo.x86_64

The only difference is that when we are using 3.x kernel from elrepo, 
the system crash never appears, just client hangs.

Mount options:
Flags: 
rw,relatime,vers=4.0,rsize=1048576,wsize=1048576,namlen=255,hard,noresvport,proto=tcp,port=0,timeo=600,retrans=2,sec=sys,clientaddr=IP,local_lock=none,addr=IP

Nfs utils version:
nfs-utils-1.2.3-15.el6_2.1.x86_64

Any ideas?
Thanks,
Barbara