1 files changed, 33 insertions, 8 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 84d13d6bb30b..1a0f10f0a4db 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1541,17 +1541,19 @@ static int wait_consider_task(struct wait_opts *wo, int ptrace,
         if (p->exit_state == EXIT_DEAD)
                 return 0;
 
-        if (likely(!ptrace) && unlikely(task_ptrace(p))) {
+        /* slay zombie? */
+        if (p->exit_state == EXIT_ZOMBIE) {
                 /*
-                 * This child is hidden by ptrace.
-                 * We aren't allowed to see it now, but eventually we will.
+                 * A zombie ptracee is only visible to its ptracer.
+                 * Notification and reaping will be cascaded to the real
+                 * parent when the ptracer detaches.
                  */
-                wo->notask_error = 0;
-                return 0;
-        }
+                if (likely(!ptrace) && unlikely(task_ptrace(p))) {
+                        /* it will become visible, clear notask_error */
+                        wo->notask_error = 0;
+                        return 0;
+                }
 
-        /* slay zombie? */
-        if (p->exit_state == EXIT_ZOMBIE) {
                 /* we don't reap group leaders with subthreads */
                 if (!delay_group_leader(p))
                         return wait_task_zombie(wo, p);
@@ -1580,15 +1582,38 @@ static int wait_consider_task(struct wait_opts *wo, int ptrace,
                         wo->notask_error = 0;
         } else {
                 /*
+                 * If @p is ptraced by a task in its real parent's group,
+                 * hide group stop/continued state when looking at @p as
+                 * the real parent; otherwise, a single stop can be
+                 * reported twice as group and ptrace stops.
+                 *
+                 * If a ptracer wants to distinguish the two events for its
+                 * own children, it should create a separate process which
+                 * takes the role of real parent.
+                 */
+                if (likely(!ptrace) && task_ptrace(p) &&
+                    same_thread_group(p->parent, p->real_parent))
+                        return 0;
+
+                /*
                  * @p is alive and it's gonna stop, continue or exit, so
                  * there always is something to wait for.
                  */
                 wo->notask_error = 0;
         }
 
+        /*
+         * Wait for stopped.  Depending on @ptrace, different stopped state
+         * is used and the two don't interact with each other.
+         */
         if (task_stopped_code(p, ptrace))
                 return wait_task_stopped(wo, ptrace, p);
 
+        /*
+         * Wait for continued.  There's only one continued state and the
+         * ptracer can consume it which can confuse the real parent.  Don't
+         * use WCONTINUED from ptracer.  You don't need or want it.
+         */
         return wait_task_continued(wo, p);
 }