kill tracehook_notify_death()

Kill tracehook_notify_death(), reimplement the logic in its caller,
exit_notify().

Also, change the exec_id's check to use thread_group_leader() instead
of task_detached(), this is more clear. This logic only applies to
the exiting leader, a sub-thread must never change its exit_signal.

Note: when the traced group leader exits the exit_signal-or-SIGCHLD
logic looks really strange:

	- we notify the tracer even if !thread_group_empty() but
	   do_wait(WEXITED) can't work until all threads exit

	- if the tracer is real_parent, it is not clear why can't
	  we use ->exit_signal event if !thread_group_empty()

-v2: do not try to fix the 2nd oddity to avoid the subtle behavior
     change mixed with reorganization, suggested by Tejun.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Tejun Heo <tj@kernel.org>

1 files changed, 13 insertions, 8 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 34d135f4fccc..bb08e938ca74 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -819,9 +819,7 @@ static void forget_original_parent(struct task_struct *father)
  */
 static void exit_notify(struct task_struct *tsk, int group_dead)
 {
-        int signal;
         bool autoreap;
-        void *cookie;
 
         /*
          * This does two things:
@@ -852,16 +850,23 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
          * we have changed execution domain as these two values started
          * the same after a fork.
          */
-        if (tsk->exit_signal != SIGCHLD && !task_detached(tsk) &&
+        if (thread_group_leader(tsk) && tsk->exit_signal != SIGCHLD &&
             (tsk->parent_exec_id != tsk->real_parent->self_exec_id ||
              tsk->self_exec_id != tsk->parent_exec_id))
                 tsk->exit_signal = SIGCHLD;
 
-        signal = tracehook_notify_death(tsk, &cookie, group_dead);
-        if (signal >= 0)
-                autoreap = do_notify_parent(tsk, signal);
-        else
-                autoreap = (signal == DEATH_REAP);
+        if (unlikely(tsk->ptrace)) {
+                int sig = thread_group_leader(tsk) &&
+                                thread_group_empty(tsk) &&
+                                !ptrace_reparented(tsk) ?
+                        tsk->exit_signal : SIGCHLD;
+                autoreap = do_notify_parent(tsk, sig);
+        } else if (thread_group_leader(tsk)) {
+                autoreap = thread_group_empty(tsk) &&
+                        do_notify_parent(tsk, tsk->exit_signal);
+        } else {
+                autoreap = true;
+        }
 
         tsk->exit_state = autoreap ? EXIT_DEAD : EXIT_ZOMBIE;