On Tue, Jan 30, 2024 at 02:44:51PM +0000, Dave Martin wrote:

I think the logic is that any ptrace call that can access or manipulate
the state of a task is gated on the task being ptrace-stopped.  Once we
have committed to deliveing a signal, we have obviously run past the
opportunity to stop (and hence be ptraced) on that signal.

This seems to be all there, the core ptrace and the signal handling code
talk to each other and ensure that we won't try to rewrite the state in
the middle of signal handling so we should be safe here.