1 files changed, 34 insertions, 10 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index b4a935c72159..84d13d6bb30b 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1550,17 +1550,41 @@ static int wait_consider_task(struct wait_opts *wo, int ptrace,
                 return 0;
         }
 
-        /*
-         * We don't reap group leaders with subthreads.
-         */
-        if (p->exit_state == EXIT_ZOMBIE && !delay_group_leader(p))
-                return wait_task_zombie(wo, p);
+        /* 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);
 
-        /*
-         * It's stopped or running now, so it might
-         * later continue, exit, or stop again.
-         */
-        wo->notask_error = 0;
+                /*
+                 * Allow access to stopped/continued state via zombie by
+                 * falling through.  Clearing of notask_error is complex.
+                 *
+                 * When !@ptrace:
+                 *
+                 * If WEXITED is set, notask_error should naturally be
+                 * cleared.  If not, subset of WSTOPPED|WCONTINUED is set,
+                 * so, if there are live subthreads, there are events to
+                 * wait for.  If all subthreads are dead, it's still safe
+                 * to clear - this function will be called again in finite
+                 * amount time once all the subthreads are released and
+                 * will then return without clearing.
+                 *
+                 * When @ptrace:
+                 *
+                 * Stopped state is per-task and thus can't change once the
+                 * target task dies.  Only continued and exited can happen.
+                 * Clear notask_error if WCONTINUED | WEXITED.
+                 */
+                if (likely(!ptrace) || (wo->wo_flags & (WCONTINUED | WEXITED)))
+                        wo->notask_error = 0;
+        } else {
+                /*
+                 * @p is alive and it's gonna stop, continue or exit, so
+                 * there always is something to wait for.
+                 */
+                wo->notask_error = 0;
+        }
 
         if (task_stopped_code(p, ptrace))
                 return wait_task_stopped(wo, ptrace, p);