ptrace_untrace: fix the SIGNAL_STOP_STOPPED check

This bug is ancient too. ptrace_untrace() must not resume the task
if the group stop in progress, we should set TASK_STOPPED instead.

Unfortunately, we still have problems here:

	- if the process/thread was traced, SIGNAL_STOP_STOPPED
	  does not necessary means this thread group is stopped.

	- ptrace breaks the bookkeeping of ->group_stop_count.

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>

1 files changed, 7 insertions, 3 deletions

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 296e8105863a..5105f5a6a2ce 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -60,11 +60,15 @@ static void ptrace_untrace(struct task_struct *child)
 {
         spin_lock(&child->sighand->siglock);
         if (task_is_traced(child)) {
-                if (child->signal->flags & SIGNAL_STOP_STOPPED) {
+                /*
+                 * If the group stop is completed or in progress,
+                 * this thread was already counted as stopped.
+                 */
+                if (child->signal->flags & SIGNAL_STOP_STOPPED ||
+                    child->signal->group_stop_count)
                         __set_task_state(child, TASK_STOPPED);
-                } else {
+                else
                         signal_wake_up(child, 1);
-                }
         }
         spin_unlock(&child->sighand->siglock);
 }