RDMA/core: Use refcount_t instead of atomic_t on refcount of mcast_port

The refcount_t API will WARN on underflow and overflow of a reference
counter, and avoid use-after-free risks.

Link: https://lore.kernel.org/r/1622194663-2383-6-git-send-email-liweihang@huawei.comSigned-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/core/multicast.c

@@ -61,7 +61,7 @@ struct mcast_port {
 	struct mcast_device	*dev;
 	spinlock_t		lock;
 	struct rb_root		table;
-	atomic_t		refcount;
+	refcount_t		refcount;
 	struct completion	comp;
 	u32			port_num;
 };
@@ -178,7 +178,7 @@ static struct mcast_group *mcast_insert(struct mcast_port *port,
 
 static void deref_port(struct mcast_port *port)
 {
-	if (atomic_dec_and_test(&port->refcount))
+	if (refcount_dec_and_test(&port->refcount))
 		complete(&port->comp);
 }
 
@@ -589,7 +589,7 @@ static struct mcast_group *acquire_group(struct mcast_port *port,
 		kfree(group);
 		group = cur_group;
 	} else
-		atomic_inc(&port->refcount);
+		refcount_inc(&port->refcount);
 found:
 	atomic_inc(&group->refcount);
 	spin_unlock_irqrestore(&port->lock, flags);
@@ -840,7 +840,7 @@ static int mcast_add_one(struct ib_device *device)
 		spin_lock_init(&port->lock);
 		port->table = RB_ROOT;
 		init_completion(&port->comp);
-		atomic_set(&port->refcount, 1);
+		refcount_set(&port->refcount, 1);
 		++count;
 	}