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>

2 files changed, 13 insertions, 42 deletions

diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index 7a1bd12aeffa..a71a2927a6a0 100644
--- a/include/linux/tracehook.h
+++ b/include/linux/tracehook.h
@@ -152,40 +152,6 @@ static inline void tracehook_signal_handler(int sig, siginfo_t *info,
                 ptrace_notify(SIGTRAP);
 }
 
-#define DEATH_REAP                      -1
-#define DEATH_DELAYED_GROUP_LEADER      -2
-
-/**
- * tracehook_notify_death - task is dead, ready to notify parent
- * @task:               @current task now exiting
- * @death_cookie:       value to pass to tracehook_report_death()
- * @group_dead:         nonzero if this was the last thread in the group to die
- *
- * A return value >= 0 means call do_notify_parent() with that signal
- * number.  Negative return value can be %DEATH_REAP to self-reap right
- * now, or %DEATH_DELAYED_GROUP_LEADER to a zombie without notifying our
- * parent.  Note that a return value of 0 means a do_notify_parent() call
- * that sends no signal, but still wakes up a parent blocked in wait*().
- *
- * Called with write_lock_irq(&tasklist_lock) held.
- */
-static inline int tracehook_notify_death(struct task_struct *task,
-                                         void **death_cookie, int group_dead)
-{
-        if (task_detached(task))
-                return task->ptrace ? SIGCHLD : DEATH_REAP;
-
-        /*
-         * If something other than our normal parent is ptracing us, then
-         * send it a SIGCHLD instead of honoring exit_signal.  exit_signal
-         * only has special meaning to our real parent.
-         */
-        if (thread_group_empty(task) && !ptrace_reparented(task))
-                return task->exit_signal;
-
-        return task->ptrace ? SIGCHLD : DEATH_DELAYED_GROUP_LEADER;
-}
-
 #ifdef TIF_NOTIFY_RESUME
 /**
  * set_notify_resume - cause tracehook_notify_resume() to be called
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;