Get rid of the cdev handle refcount.

We only create one VM cdev object per GEM object, and the VM object
destructor runs only once all of its references are gone.

Author: markjdb

sys/compat/linuxkpi/common/src/linux_compat.c

@@ -737,8 +737,8 @@ linux_cdev_pager_populate(vm_object_t vm_obj, vm_pindex_t pidx, int fault_type,
 }
 
 struct list_head lcdev_handle_list;
+
 struct lcdev_handle_ref {
-	volatile int refcnt;
 	void *handle;
 	void *data;
 	struct list_head list;
@@ -754,23 +754,20 @@ linux_cdev_handle_insert(void *handle, void *data, int size)
 	rw_rlock(&linux_global_rw);
 	list_for_each(h, &lcdev_handle_list) {
 		r = __containerof(h, struct lcdev_handle_ref, list);
-		if (r->handle == handle)
-			break;
-	}
-	if (r && r->handle == handle) {
-		atomic_add_int(&r->refcnt, 1);
-		rw_runlock(&linux_global_rw);
-		return;
+		if (r->handle == handle) {
+			rw_runlock(&linux_global_rw);
+			return;
+		}
 	}
 	rw_runlock(&linux_global_rw);
 	r = lkpi_malloc(sizeof(struct lcdev_handle_ref), M_KMALLOC, M_WAITOK);
-	r->refcnt = 1;
 	r->handle = handle;
 	datap = lkpi_malloc(size, M_KMALLOC, M_WAITOK);
 	memcpy(datap, data, size);
 	r->data = datap;
-	INIT_LIST_HEAD(&r->list);
+	INIT_LIST_HEAD(&r->list); /* XXX why _HEAD? */
 	rw_wlock(&linux_global_rw);
+	/* XXX need to re-lookup */
 	list_add_tail(&r->list, &lcdev_handle_list);
 	rw_wunlock(&linux_global_rw);
 }
@@ -788,13 +785,10 @@ linux_cdev_handle_remove(void *handle)
 			break;
 	}
 	MPASS (r && r->handle == handle);
-	if (atomic_fetchadd_int(&r->refcnt, -1) == 0) {
-		list_del(&r->list);
-		rw_wunlock(&linux_global_rw);
-		lkpi_free(r->data, M_KMALLOC);
-		lkpi_free(r, M_KMALLOC);
-	} else
-		rw_wunlock(&linux_global_rw);
+	list_del(&r->list);
+	rw_wunlock(&linux_global_rw);
+	lkpi_free(r->data, M_KMALLOC);
+	lkpi_free(r, M_KMALLOC);
 }
 
 static void *