RDS: cleanup/fix rds_rdma_unuse

First, it looks to me like the atomic_inc is wrong.
We should be decrementing refcount only once here, no? It's
already being done by the mr_put() at the end.

Second, simplify the logic a bit by bailing early (with a warning)
if !mr.
Signed-off-by: Andy Grover <andy.grover@oracle.com>

net/rds/rdma.c

@@ -414,18 +414,22 @@ void rds_rdma_unuse(struct rds_sock *rs, u32 r_key, int force)
 
 	spin_lock_irqsave(&rs->rs_rdma_lock, flags);
 	mr = rds_mr_tree_walk(&rs->rs_rdma_keys, r_key, NULL);
-	if (mr && (mr->r_use_once || force)) {
+	if (!mr) {
+		printk(KERN_ERR "rds: trying to unuse MR with unknown r_key %u!\n", r_key);
+		spin_unlock_irqrestore(&rs->rs_rdma_lock, flags);
+		return;
+	}
+
+	if (mr->r_use_once || force) {
 		rb_erase(&mr->r_rb_node, &rs->rs_rdma_keys);
 		RB_CLEAR_NODE(&mr->r_rb_node);
 		zot_me = 1;
-	} else if (mr)
-		atomic_inc(&mr->r_refcount);
+	}
 	spin_unlock_irqrestore(&rs->rs_rdma_lock, flags);
 
 	/* May have to issue a dma_sync on this memory region.
 	 * Note we could avoid this if the operation was a RDMA READ,
 	 * but at this point we can't tell. */
-	if (mr) {
 	if (mr->r_trans->sync_mr)
 		mr->r_trans->sync_mr(mr->r_trans_private, DMA_FROM_DEVICE);
 
@@ -434,7 +438,6 @@ void rds_rdma_unuse(struct rds_sock *rs, u32 r_key, int force)
 	if (zot_me)
 		rds_destroy_mr(mr);
 	rds_mr_put(mr);
-	}
 }
 
 void rds_rdma_free_op(struct rds_rdma_op *ro)