On Mon, Jun 21, 2021 at 4:23 PM Al Viro [off-list ref] wrote:

        How would it help e.g. oopsen on the way out of timer interrupts?
IMO we simply shouldn't allow ptrace access if the tracee is in that kind
of state, on any architecture...

Yeah no, we can't do the "wait for ptrace" when the exit is due to an
oops. Although honestly, we have other cases like that where do_exit()
isn't 100% robust if you kill something in an interrupt. Like all the
locks it leaves locked etc.

So do_exit() from a timer interrupt is going to cause problems
regardless. I agree it's probably a good idea to try to avoid causing
even more with the odd ptrace thing, but I don't think ptrace_event is
some really "fundamental" problem at that point - it's just one detail
among many many.

So I was more thinking of the debug patch for m68k to catch all the
_regular_ cases, and all the other random cases of ptrace_event() or
ptrace_notify().

Although maybe we've really caught them all. The exit case was clearly
missing, and the thread fork case was scrogged. There are patches for
the known problems. The patches I really don't like are the
verification ones to find any unknown ones..

            Linus