ptrace: reintroduce __ptrace_detach() as a callee of ptrace_exit()

No functional changes, preparation for the next patch.

Move the "should we release this child" logic into the separate handler,
__ptrace_detach().
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/exit.c

@@ -744,48 +744,52 @@ static int ignoring_children(struct sighand_struct *sigh)
 	return ret;
 }
 
-/*
- * Detach all tasks we were using ptrace on.
- * Any that need to be release_task'd are put on the @dead list.
- *
- * Called with write_lock(&tasklist_lock) held.
- */
-static void ptrace_exit(struct task_struct *parent, struct list_head *dead)
+/* Returns nonzero if the tracee should be released. */
+int __ptrace_detach(struct task_struct *tracer, struct task_struct *p)
 {
-	struct task_struct *p, *n;
-
-	list_for_each_entry_safe(p, n, &parent->ptraced, ptrace_entry) {
 	__ptrace_unlink(p);
 
 	if (p->exit_state != EXIT_ZOMBIE)
-			continue;
-
+		return 0;
 	/*
 	 * If it's a zombie, our attachedness prevented normal
 	 * parent notification or self-reaping.  Do notification
 	 * now if it would have happened earlier.  If it should
-		 * reap itself, add it to the @dead list.  We can't call
-		 * release_task() here because we already hold tasklist_lock.
+	 * reap itself we return true.
 	 *
 	 * If it's our own child, there is no notification to do.
 	 * But if our normal children self-reap, then this child
 	 * was prevented by ptrace and we must reap it now.
 	 */
 	if (!task_detached(p) && thread_group_empty(p)) {
-			if (!same_thread_group(p->real_parent, parent))
+		if (!same_thread_group(p->real_parent, tracer))
 			do_notify_parent(p, p->exit_signal);
-			else if (ignoring_children(parent->sighand))
+		else if (ignoring_children(tracer->sighand))
 			p->exit_signal = -1;
 	}
 
-		if (task_detached(p)) {
-			/*
-			 * Mark it as in the process of being reaped.
-			 */
+	if (!task_detached(p))
+		return 0;
+
+	/* Mark it as in the process of being reaped. */
 	p->exit_state = EXIT_DEAD;
+	return 1;
+}
+
+/*
+ * Detach all tasks we were using ptrace on.
+ * Any that need to be release_task'd are put on the @dead list.
+ *
+ * Called with write_lock(&tasklist_lock) held.
+ */
+static void ptrace_exit(struct task_struct *parent, struct list_head *dead)
+{
+	struct task_struct *p, *n;
+
+	list_for_each_entry_safe(p, n, &parent->ptraced, ptrace_entry) {
+		if (__ptrace_detach(parent, p))
 			list_add(&p->ptrace_entry, dead);
 	}
-	}
 }
 
 /*