Re: [PATCH] Fix segmentation fault and infinite loop in jsonb_{plperl,plpython}

Aleksander Alekseev <aleksander(at)tigerdata(dot)com> writes:
> The second bug affects only jsonb_plperl. It's possible to construct a
> Perl object with circular references which will cause
> SV_to_JsonbValue() to go into an infinite loop here:

> while (SvROK(in))
> in = SvRV(in);

> I suggest fixing it by rewriting the while loop into a recursion with
> check_stack_depth() call. This will make the behavior consistent with
> jsonb_plpython.

Unfortunately, your 0002 is too cute for its own good. I tried it
here, with a not-especially-new gcc compiling at -O2, and found that
the tail recursion in SV_deref() is optimized into a loop. So the
stack doesn't grow and we still have an uninterruptible loop.

I don't immediately see a way to write that function so that the
compiler is certain not to spot the tail recursion. Tricks like
two mutually recursive functions might be seen through at
sufficiently high -O levels.

We could instead add a CHECK_FOR_INTERRUPTS, so that you can at
least break out of the infinite loop. I'm not sure if the case
is worth more effort than that.

regards, tom lane