use __set_task_state() for TRACED/STOPPED tasks

1. It is much easier to grep for ->state change if __set_task_state() is used
   instead of the direct assignment.

2. ptrace_stop() and handle_group_stop() use set_task_state() which adds the
   unneeded mb() (btw even if we use mb() it is still possible that do_wait()
   sees the new ->state but not ->exit_code, but this is ok).

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/fork.c

@@ -1510,7 +1510,7 @@ long do_fork(unsigned long clone_flags,
 		if (!(clone_flags & CLONE_STOPPED))
 			wake_up_new_task(p, clone_flags);
 		else
-			p->state = TASK_STOPPED;
+			__set_task_state(p, TASK_STOPPED);
 
 		if (unlikely (trace)) {
 			current->ptrace_message = nr;

kernel/ptrace.c

@@ -53,7 +53,7 @@ void ptrace_untrace(struct task_struct *child)
 	spin_lock(&child->sighand->siglock);
 	if (task_is_traced(child)) {
 		if (child->signal->flags & SIGNAL_STOP_STOPPED) {
-			child->state = TASK_STOPPED;
+			__set_task_state(child, TASK_STOPPED);
 		} else {
 			signal_wake_up(child, 1);
 		}
@@ -103,18 +103,16 @@ int ptrace_check_attach(struct task_struct *child, int kill)
 	    && child->signal != NULL) {
 		ret = 0;
 		spin_lock_irq(&child->sighand->siglock);
-		if (task_is_stopped(child)) {
+		if (task_is_stopped(child))
 			child->state = TASK_TRACED;
-		} else if (!task_is_traced(child) && !kill) {
+		else if (!task_is_traced(child) && !kill)
 			ret = -ESRCH;
-		}
 		spin_unlock_irq(&child->sighand->siglock);
 	}
 	read_unlock(&tasklist_lock);
 
-	if (!ret && !kill) {
+	if (!ret && !kill)
 		wait_task_inactive(child);
-	}
 
 	/* All systems go.. */
 	return ret;

kernel/signal.c

@@ -1601,7 +1601,7 @@ static void ptrace_stop(int exit_code, int nostop_code, siginfo_t *info)
 	current->exit_code = exit_code;
 
 	/* Let the debugger run.  */
-	set_current_state(TASK_TRACED);
+	__set_current_state(TASK_TRACED);
 	spin_unlock_irq(&current->sighand->siglock);
 	try_to_freeze();
 	read_lock(&tasklist_lock);