There is a couple of subtle checks which were needed to handle ptracing from

the same thread group. This was deprecated a long ago, imho this code just

complicates the understanding.
And, the "->parent->signal->flags & SIGNAL_GROUP_EXIT" check in exit_notify()

is not right. SIGNAL_GROUP_EXIT can mean exec(), not exit_group(). This means

ptracer can lose a ptraced zombie on exec(). Minor problem, but still the bug.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
--- t/kernel/exit.c~PT_TG	2007-08-03 18:05:52.000000000 +0400

+++ t/kernel/exit.c	2007-08-03 21:10:40.000000000 +0400

@@ -802,7 +802,7 @@ static void exit_notify(struct task_stru

 		__kill_pgrp_info(SIGCONT, SEND_SIG_PRIV, pgrp);

 	}
-	/* Let father know we died

+	/* Let father know we died

 	 *

 	 * Thread signals are configurable, but you aren't going to use

 	 * that to send signals to arbitary processes.

@@ -815,9 +815,7 @@ static void exit_notify(struct task_stru

 	 * If our self_exec id doesn't match our parent_exec_id then

 	 * we have changed execution domain as these two values started

 	 * the same after a fork.

-	 *

 	 */

-

 	if (tsk->exit_signal != SIGCHLD && tsk->exit_signal != -1 &&

 	    ( tsk->parent_exec_id != t->self_exec_id  ||

 	      tsk->self_exec_id != tsk->parent_exec_id)

@@ -837,9 +835,7 @@ static void exit_notify(struct task_stru

 	}
 	state = EXIT_ZOMBIE;

-	if (tsk->exit_signal == -1 &&

-	    (likely(tsk->ptrace == 0) ||

-	     unlikely(tsk->parent->signal->flags & SIGNAL_GROUP_EXIT)))

+	if (tsk->exit_signal == -1 && likely(!tsk->ptrace))

 		state = EXIT_DEAD;

 	tsk->exit_state = state;
--- t/kernel/signal.c~PT_TG	2007-07-28 16:58:17.000000000 +0400

+++ t/kernel/signal.c	2007-08-03 21:11:59.000000000 +0400

@@ -1561,10 +1561,6 @@ static inline int may_ptrace_stop(void)

 		    (current->ptrace & PT_ATTACHED)))

 		return 0;
-	if (unlikely(current->signal == current-&...
[ message continues ]

This bug never happens because this check is only in the now-impossible

ptrace-same-group case.  The code can certainly go.
Thanks,

Roland

-

This means that changelog is wrong and should be changed.
However, I disagree. exit_notify() doesn't check the ptrace-same-group case. So,

unless I missed something, we set EXIT_DEAD in any case, even if ptracer doesn't

belong to our thread group.
No?
Oleg.
-

Oh, you're right.  I was reading the other line you changed.
Thanks,

Roland

-