[PATCH] utrace_stop: don't forget about SIGNAL_STOP_STOPPED

[Oleg Nesterov]

utrace_stop() decrements ->group_stop_count but doesn't set
SIGNAL_STOP_STOPPED if we are the last thread. This breaks
utrace_wakeup() logic.

Perhaps we need more changes here, but I think this one is
most important.

Signed-off-by: Oleg Nesterov <o...@redhat.com>

--- __UTRACE/kernel/utrace.c~UTRACE_STOP_SSS    2009-07-28 21:55:43.000000000 
+0200
+++ __UTRACE/kernel/utrace.c    2009-07-28 22:12:44.000000000 +0200
@@ -416,8 +416,9 @@ static bool utrace_stop(struct task_stru
         * If there is a group stop in progress,
         * we must participate in the bookkeeping.
         */
-       if (task->signal->group_stop_count > 0)
-               --task->signal->group_stop_count;
+       if (unlikely(task->signal->group_stop_count) &&
+                       !--task->signal->group_stop_count)
+               task->signal->flags = SIGNAL_STOP_STOPPED;
 
        spin_unlock_irq(&task->sighand->siglock);
        spin_unlock(&utrace->lock);