[PATCH 4/4] ptrace: ptrace_check_attach() should not do s/STOPPED/TRACED/

[Oleg Nesterov <oleg@redhat.com>]

After "ptrace: Clean transitions between TASK_STOPPED and TRACED"
d79fdd6d96f46fabb779d86332e3677c6f5c2a4f, ptrace_check_attach()
should never see a TASK_STOPPED tracee and s/STOPPED/TRACED/ is
no longer legal. Add the warning.

Note: ptrace_check_attach() can be greatly simplified, in particular
it doesn't need tasklist. But I'd prefer another patch for that.

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

 kernel/ptrace.c |    8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

--- ptrace/kernel/ptrace.c~4_ck_attach_cant_be_stopped	2011-04-01 16:36:29.000000000 +0200
+++ ptrace/kernel/ptrace.c	2011-04-01 19:54:05.000000000 +0200
@@ -112,16 +112,14 @@ int ptrace_check_attach(struct task_stru
 	 */
 	read_lock(&tasklist_lock);
 	if ((child->ptrace & PT_PTRACED) && child->parent == current) {
-		ret = 0;
 		/*
 		 * child->sighand can't be NULL, release_task()
 		 * does ptrace_unlink() before __exit_signal().
 		 */
 		spin_lock_irq(&child->sighand->siglock);
-		if (task_is_stopped(child))
-			child->state = TASK_TRACED;
-		else if (!task_is_traced(child) && !kill)
-			ret = -ESRCH;
+		WARN_ON_ONCE(task_is_stopped(child));
+		if (task_is_traced(child) || kill)
+			ret = 0;
 		spin_unlock_irq(&child->sighand->siglock);
 	}
 	read_unlock(&tasklist_lock);