ptrace and kernel threads

H i all, You will get an error when trying to call ptrace system call on kernel threads. In code, you have the following check: static int ptrace_attach(struct task_struct *task, long request, unsigned long addr, unsigned long flags) { ... retval = -EPERM; if (unlikely(task->flags & PF_KTHREAD)) goto out; ... see: http://lxr.free-electrons.com/source/kernel/ptrace.c#L233 Question: what is the reason that kernel threads cannot be traced while userspace threads can be traced ? rgs, Kevin