ptrace: ptrace_check_attach() should not do s/STOPPED/TRACED/

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>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 3 insertions, 5 deletions

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 43485866749a..20d5efdeee02 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -112,16 +112,14 @@ int ptrace_check_attach(struct task_struct *child, int kill)
          */
         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);