[PATCH] remove BUG_ON(p->ptrace) in release_task()

The BUG_ON(p->ptrace) will be called if the CLONE_DETACH process is
traced.  This patch removes BUG_ON(p->ptrace), and also removes a
workaround for it in sys_wait4().

kernel/exit.c

@@ -66,8 +66,7 @@ static void release_task(struct task_struct * p)
 	atomic_dec(&p->user->processes);
 	security_ops->task_free_security(p);
 	free_uid(p->user);
-	BUG_ON(p->ptrace || !list_empty(&p->ptrace_list) ||
-					!list_empty(&p->ptrace_children));
+	BUG_ON(!list_empty(&p->ptrace_list) || !list_empty(&p->ptrace_children));
 	unhash_process(p);
 
 	release_thread(p);
@@ -717,14 +716,8 @@ asmlinkage long sys_wait4(pid_t pid,unsigned int * stat_addr, int options, struc
 					ptrace_unlink(p);
 					do_notify_parent(p, SIGCHLD);
 					write_unlock_irq(&tasklist_lock);
-				} else {
-					if (p->ptrace) {
-						write_lock_irq(&tasklist_lock);
-						ptrace_unlink(p);
-						write_unlock_irq(&tasklist_lock);
-					}
+				} else
 					release_task(p);
-				}
 				goto end_wait4;
 			default:
 				continue;