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

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/[e-mail]
Signed-off-by: Weihang Li <[e-mail]>
Signed-off-by: Jason Gunthorpe <[e-mail]>

drivers/infiniband/core/iwcm.c

···
  */
 static int iwcm_deref_id(struct iwcm_id_private *cm_id_priv)
 {
-	BUG_ON(atomic_read(&cm_id_priv->refcount)==0);
-	if (atomic_dec_and_test(&cm_id_priv->refcount)) {
+	if (refcount_dec_and_test(&cm_id_priv->refcount)) {
 		BUG_ON(!list_empty(&cm_id_priv->work_list));
 		free_cm_id(cm_id_priv);
 		return 1;
···
 {
 	struct iwcm_id_private *cm_id_priv;
 	cm_id_priv = container_of(cm_id, struct iwcm_id_private, id);
-	atomic_inc(&cm_id_priv->refcount);
+	refcount_inc(&cm_id_priv->refcount);
 }
 
 static void rem_ref(struct iw_cm_id *cm_id)
···
 	cm_id_priv->id.add_ref = add_ref;
 	cm_id_priv->id.rem_ref = rem_ref;
 	spin_lock_init(&cm_id_priv->lock);
-	atomic_set(&cm_id_priv->refcount, 1);
+	refcount_set(&cm_id_priv->refcount, 1);
 	init_waitqueue_head(&cm_id_priv->connect_wait);
 	init_completion(&cm_id_priv->destroy_comp);
 	INIT_LIST_HEAD(&cm_id_priv->work_list);
···
 		}
 	}
 
-	atomic_inc(&cm_id_priv->refcount);
+	refcount_inc(&cm_id_priv->refcount);
 	if (list_empty(&cm_id_priv->work_list)) {
 		list_add_tail(&work->list, &cm_id_priv->work_list);
 		queue_work(iwcm_wq, &work->work);

drivers/infiniband/core/iwcm.h

···
 	wait_queue_head_t connect_wait;
 	struct list_head work_list;
 	spinlock_t lock;
-	atomic_t refcount;
+	refcount_t refcount;
 	struct list_head work_free_list;
 };