radix tree test suite: Register the main thread with the RCU library

Several test runners register individual worker threads with the
RCU library, but neglect to register the main thread, which can lead
to objects being freed while the main thread is in what appears to be
an RCU critical section.
Reported-by: Chris von Recklinghausen <crecklin@redhat.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

tools/testing/radix-tree/idr-test.c

@@ -577,6 +577,7 @@ void ida_tests(void)
 
 int __weak main(void)
 {
+	rcu_register_thread();
 	radix_tree_init();
 	idr_checks();
 	ida_tests();
@@ -584,5 +585,6 @@ int __weak main(void)
 	rcu_barrier();
 	if (nr_allocated)
 		printf("nr_allocated = %d\n", nr_allocated);
+	rcu_unregister_thread();
 	return 0;
 }

tools/testing/radix-tree/multiorder.c

@@ -224,7 +224,9 @@ void multiorder_checks(void)
 
 int __weak main(void)
 {
+	rcu_register_thread();
 	radix_tree_init();
 	multiorder_checks();
+	rcu_unregister_thread();
 	return 0;
 }

tools/testing/radix-tree/xarray.c

@@ -25,11 +25,13 @@ void xarray_tests(void)
 
 int __weak main(void)
 {
+	rcu_register_thread();
 	radix_tree_init();
 	xarray_tests();
 	radix_tree_cpu_dead(1);
 	rcu_barrier();
 	if (nr_allocated)
 		printf("nr_allocated = %d\n", nr_allocated);
+	rcu_unregister_thread();
 	return 0;
 }