wait: use EXIT_TRACE only if thread_group_leader(zombie)

oleg-nesterov · torvalds · commit b436069059fe · 2014-04-07T16:36:05.000-07:00
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-&gt;exit_state transition.

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