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Subject[PATCH] kill an obsolete sub-thread-ptrace stuff
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->parent->signal) &&
- unlikely(current->signal->flags & SIGNAL_GROUP_EXIT))
- return 0;
-
/*
* Are we in the middle of do_coredump?
* If so and our tracer is also part of the coredump stopping
-
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