perf machine: Mark removed threads as such

We use:

  BUG_ON(!RB_EMPTY_NODE(&thread->rb_node));

in the thread destructor as a debugging check to find out about
possibly still referenced thread instances being deleted, to do that
we need to make sure we use RB_CLEAR_NODE() right after rb_erase(),
i.e. that we use the newly introduced rb_erase_init(), that works
just like list_del_init().

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-4fcqo5ypy1cjjf15ilb0hn78@git.kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/machine.c

@@ -400,7 +400,7 @@ static struct thread *____machine__findnew_thread(struct machine *machine,
 		 * leader and that would screwed the rb tree.
 		 */
 		if (thread__init_map_groups(th, machine)) {
-			rb_erase(&th->rb_node, &machine->threads);
+			rb_erase_init(&th->rb_node, &machine->threads);
 			RB_CLEAR_NODE(&th->rb_node);
 			thread__delete(th);
 			return NULL;
@@ -1314,7 +1314,7 @@ static void __machine__remove_thread(struct machine *machine, struct thread *th,
 	BUG_ON(atomic_read(&th->refcnt) == 0);
 	if (lock)
 		pthread_rwlock_wrlock(&machine->threads_lock);
-	rb_erase(&th->rb_node, &machine->threads);
+	rb_erase_init(&th->rb_node, &machine->threads);
 	RB_CLEAR_NODE(&th->rb_node);
 	/*
 	 * Move it first to the dead_threads list, then drop the reference,