perfcounters: fix refcounting bug, take 2

Only free child_counter if it has a parent; if it doesn't, then it
has a file pointing to it and we'll free it in perf_release.
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/perf_counter.c

@@ -1958,14 +1958,13 @@ __perf_counter_exit_task(struct task_struct *child,
 		sync_child_counter(child_counter, parent_counter);
 		list_for_each_entry_safe(sub, tmp, &child_counter->sibling_list,
 					 list_entry) {
-			if (sub->parent)
+			if (sub->parent) {
 				sync_child_counter(sub, sub->parent);
-			kfree(sub);
+				kfree(sub);
+			}
 		}
-	}
-
-	if (!child_counter->filp || !atomic_long_read(&child_counter->filp->f_count))
 		kfree(child_counter);
+	}
 }
 
 /*