wait: use EXIT_TRACE only if thread_group_leader(zombie)

wait_task_zombie() always uses EXIT_TRACE/ptrace_unlink() if
ptrace_reparented().  This is suboptimal and a bit confusing: we do not
need do_notify_parent(p) if !thread_group_leader(p) and in this case we
also do not need ptrace_unlink(), we can rely on ptrace_release_task().

Change wait_task_zombie() to check thread_group_leader() along with
ptrace_reparented() and simplify the final p->exit_state transition.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Tested-by: Michal Schmidt <mschmidt@redhat.com>
Cc: Jan Kratochvil <jan.kratochvil@redhat.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Lennart Poettering <lpoetter@redhat.com>
Cc: Roland McGrath <roland@hack.frob.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 10 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 022a0ff17318..4773ed990907 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1040,7 +1040,7 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
         /*
          * Move the task's state to DEAD/TRACE, only one thread can do this.
          */
-        state = traced ? EXIT_TRACE : EXIT_DEAD;
+        state = traced && thread_group_leader(p) ? EXIT_TRACE : EXIT_DEAD;
         if (cmpxchg(&p->exit_state, EXIT_ZOMBIE, state) != EXIT_ZOMBIE)
                 return 0;
         /*
@@ -1140,18 +1140,15 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
         if (!retval)
                 retval = pid;
 
-        if (traced) {
+        if (state == EXIT_TRACE) {
                 write_lock_irq(&tasklist_lock);
                 /* We dropped tasklist, ptracer could die and untrace */
                 ptrace_unlink(p);
-                /*
-                 * If this is not a sub-thread, notify the parent.
-                 * If parent wants a zombie, don't release it now.
-                 */
-                state = EXIT_DEAD;
-                if (thread_group_leader(p) &&
-                    !do_notify_parent(p, p->exit_signal))
-                        state = EXIT_ZOMBIE;
+
+                /* If parent wants a zombie, don't release it now */
+                state = EXIT_ZOMBIE;
+                if (do_notify_parent(p, p->exit_signal))
+                        state = EXIT_DEAD;
                 p->exit_state = state;
                 write_unlock_irq(&tasklist_lock);
         }