SUNRPC: Partial revert of commit 168e4b3

Partially revert commit (SUNRPC: add WARN_ON_ONCE for potential deadlock).
The looping behaviour has been tracked down to a knownn issue with
workqueues, and a workaround has now been implemented.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Weston Andros Adamson <dros@netapp.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Bruce Fields <bfields@fieldses.org>
Cc: stable@vger.kernel.org [>= 3.7]

net/sunrpc/clnt.c

@@ -610,11 +610,6 @@ EXPORT_SYMBOL_GPL(rpc_killall_tasks);
  */
 void rpc_shutdown_client(struct rpc_clnt *clnt)
 {
-	/*
-	 * To avoid deadlock, never call rpc_shutdown_client from a
-	 * workqueue context!
-	 */
-	WARN_ON_ONCE(current->flags & PF_WQ_WORKER);
 	might_sleep();
 
 	dprintk_rcu("RPC:       shutting down %s client for %s\n",