__ptrace_unlink: kill the obsolete "FIXME" code

The corner case described by the comment is no longer possible after the
commit 7b3c36fc ("ptrace: fix task_join_group_stop() for the case when
current is traced"), task_join_group_stop() ensures that the new thread
has the correct signr in JOBCTL_STOP_SIGMASK regardless of ptrace.

Link: https://lkml.kernel.org/r/20231121162650.GA6635@redhat.comSigned-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

kernel/ptrace.c

@@ -145,20 +145,9 @@ void __ptrace_unlink(struct task_struct *child)
 	 */
 	if (!(child->flags & PF_EXITING) &&
 	    (child->signal->flags & SIGNAL_STOP_STOPPED ||
-	     child->signal->group_stop_count)) {
+	     child->signal->group_stop_count))
 		child->jobctl |= JOBCTL_STOP_PENDING;
 
-		/*
-		 * This is only possible if this thread was cloned by the
-		 * traced task running in the stopped group, set the signal
-		 * for the future reports.
-		 * FIXME: we should change ptrace_init_task() to handle this
-		 * case.
-		 */
-		if (!(child->jobctl & JOBCTL_STOP_SIGMASK))
-			child->jobctl |= SIGSTOP;
-	}
-
 	/*
 	 * If transition to TASK_STOPPED is pending or in TASK_TRACED, kick
 	 * @child in the butt.  Note that @resume should be used iff @child