Q: ptrace_signal() && PTRACE_SETSIGINFO (Was: SIGSTOP && ptrace)

[Oleg Nesterov <oleg@redhat.com>]

ptrace_signal:

	signr = current->exit_code;

	/* Update the siginfo structure if the signal has
	   changed.  If the debugger wanted something
	   specific in the siginfo structure then it should
	   have updated *info via PTRACE_SETSIGINFO.  */

Yes. PTRACE_SETSIGINFO can change *info if debugger wants something
special. But then we do:

	if (signr != info->si_signo) {
		info->si_signo = signr;
		info->si_errno = 0;
		info->si_code = SI_USER;
		info->si_pid = task_pid_vnr(current->parent);
		info->si_uid = task_uid(current->parent);
	}

Why? If the tracer changes ->exit_code it should know what it does.
Why do we reset *info?

But the real question, how can PTRACE_SETSIGINFO change ->si_signo
(for example, for do_signal_stop(si_signo)) if this in fact is not
allowed?

Oleg.