Trace speaks for itself.

Sep 28 20:24:26 localhost kernel: Badness in
interruptible_sleep_on_timeout at kernel/sched.c:3004
Sep 28 20:24:26 localhost kernel:
Sep 28 20:24:26 localhost kernel: Call
Trace:<ffffffff803468e0>{interruptible_sleep_on_timeout+117}
Sep 28 20:24:26 localhost kernel:       
<ffffffff80132730>{default_wake_function+0}
<ffffffff80144677>{kill_proc_info+38}
Sep 28 20:24:26 localhost kernel:       
<ffffffffa02af2ed>{:lockd:lockd_down+199}
<ffffffffa02c768e>{:nfs:nfs_kill_super+77}
Sep 28 20:24:26 localhost kernel:       
<ffffffff8018c584>{deactivate_super+220}
<ffffffff801add0f>{sys_umount+2362}
Sep 28 20:24:26 localhost kernel:        <ffffffff801a29d7>{dput+55}
<ffffffff801866a6>{__fput+234}
Sep 28 20:24:26 localhost kernel:       
<ffffffff80184b97>{filp_close+103} <ffffffff80110782>{system_call+126}