nfs41: sunrpc: xprt_alloc_bc_request() should not use spin_lock_bh()

xprt_alloc_bc_request() is always called in soft interrupt context.
Grab the spin_lock instead of the bottom half spin_lock.  Softirqs
do not preempt other softirqs running on the same processor, so there
is no need to disable bottom halves.

Signed-off-by: Ricardo Labiaga <Ricardo.Labiaga@netapp.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/backchannel_rqst.c

@@ -211,22 +211,25 @@ EXPORT_SYMBOL(xprt_destroy_backchannel);
  * has been preallocated as well.  Use xprt_alloc_bc_request to allocate
  * to this request.  Use xprt_free_bc_request to return it.
  *
+ * We know that we're called in soft interrupt context, grab the spin_lock
+ * since there is no need to grab the bottom half spin_lock.
+ *
  * Return an available rpc_rqst, otherwise NULL if non are available.
  */
 struct rpc_rqst *xprt_alloc_bc_request(struct rpc_xprt *xprt)
 {
 	struct rpc_rqst *req;
 
 	dprintk("RPC:       allocate a backchannel request\n");
-	spin_lock_bh(&xprt->bc_pa_lock);
+	spin_lock(&xprt->bc_pa_lock);
 	if (!list_empty(&xprt->bc_pa_list)) {
 		req = list_first_entry(&xprt->bc_pa_list, struct rpc_rqst,
 				rq_bc_pa_list);
 		list_del(&req->rq_bc_pa_list);
 	} else {
 		req = NULL;
 	}
-	spin_unlock_bh(&xprt->bc_pa_lock);
+	spin_unlock(&xprt->bc_pa_lock);
 
 	if (req != NULL) {
 		set_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state);