xprtrdma: Simplify rpcrdma_mr_pop

Clean up: rpcrdma_mr_pop call sites check if the list is empty
first. Let's replace the list_empty with less costly logic.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/xprtrdma/frwr_ops.c

@@ -126,12 +126,10 @@ frwr_mr_recycle_worker(struct work_struct *work)
  */
 void frwr_reset(struct rpcrdma_req *req)
 {
-	while (!list_empty(&req->rl_registered)) {
-		struct rpcrdma_mr *mr;
+	struct rpcrdma_mr *mr;
 
-		mr = rpcrdma_mr_pop(&req->rl_registered);
+	while ((mr = rpcrdma_mr_pop(&req->rl_registered)))
 		rpcrdma_mr_unmap_and_put(mr);
-	}
 }
 
 /**
@@ -532,8 +530,7 @@ void frwr_unmap_sync(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req)
 	 */
 	frwr = NULL;
 	prev = &first;
-	while (!list_empty(&req->rl_registered)) {
-		mr = rpcrdma_mr_pop(&req->rl_registered);
+	while ((mr = rpcrdma_mr_pop(&req->rl_registered))) {
 
 		trace_xprtrdma_mr_localinv(mr);
 		r_xprt->rx_stats.local_inv_needed++;
@@ -632,8 +629,7 @@ void frwr_unmap_async(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req)
 	 */
 	frwr = NULL;
 	prev = &first;
-	while (!list_empty(&req->rl_registered)) {
-		mr = rpcrdma_mr_pop(&req->rl_registered);
+	while ((mr = rpcrdma_mr_pop(&req->rl_registered))) {
 
 		trace_xprtrdma_mr_localinv(mr);
 		r_xprt->rx_stats.local_inv_needed++;

net/sunrpc/xprtrdma/rpc_rdma.c

@@ -841,12 +841,7 @@ rpcrdma_marshal_req(struct rpcrdma_xprt *r_xprt, struct rpc_rqst *rqst)
 	 * chunks. Very likely the connection has been replaced,
 	 * so these registrations are invalid and unusable.
 	 */
-	while (unlikely(!list_empty(&req->rl_registered))) {
-		struct rpcrdma_mr *mr;
-
-		mr = rpcrdma_mr_pop(&req->rl_registered);
-		rpcrdma_mr_recycle(mr);
-	}
+	frwr_reset(req);
 
 	/* This implementation supports the following combinations
 	 * of chunk lists in one RPC-over-RDMA Call message:

net/sunrpc/xprtrdma/verbs.c

@@ -1213,13 +1213,11 @@ struct rpcrdma_mr *
 rpcrdma_mr_get(struct rpcrdma_xprt *r_xprt)
 {
 	struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
-	struct rpcrdma_mr *mr = NULL;
+	struct rpcrdma_mr *mr;
 
 	spin_lock(&buf->rb_mrlock);
-	if (!list_empty(&buf->rb_mrs))
-		mr = rpcrdma_mr_pop(&buf->rb_mrs);
+	mr = rpcrdma_mr_pop(&buf->rb_mrs);
 	spin_unlock(&buf->rb_mrlock);
-
 	if (!mr)
 		goto out_nomrs;
 	return mr;

net/sunrpc/xprtrdma/xprt_rdma.h

@@ -338,7 +338,7 @@ rpcr_to_rdmar(const struct rpc_rqst *rqst)
 static inline void
 rpcrdma_mr_push(struct rpcrdma_mr *mr, struct list_head *list)
 {
-	list_add_tail(&mr->mr_list, list);
+	list_add(&mr->mr_list, list);
 }
 
 static inline struct rpcrdma_mr *
@@ -346,8 +346,9 @@ rpcrdma_mr_pop(struct list_head *list)
 {
 	struct rpcrdma_mr *mr;
 
-	mr = list_first_entry(list, struct rpcrdma_mr, mr_list);
-	list_del_init(&mr->mr_list);
+	mr = list_first_entry_or_null(list, struct rpcrdma_mr, mr_list);
+	if (mr)
+		list_del_init(&mr->mr_list);
 	return mr;
 }