gh-153364: Limit frame, coroutine, and task-waiter chain walks

[maurycy]

The PR hardens and cleans up chain walks a bit.

It introduces a const (MAX_FRAME_CHAIN_DEPTH), uses it in the existing process_frame_chain(), which is called by get_stack_trace(), as well as adds it to parse_coro_chain(), used in both sync and async pathways, and to parse_async_frame_chain().

Also, it adds MAX_TASK_WAITER_CHAIN_DEPTH for the purpose of task-waiter limits in get_async_stack_trace().

The obvious context here is avoiding infinite loops. Truth be told, I think that in some places it unexpectedly works (ie: doesn't hang) because incomplete / torn-reads result in an exception. :-)

• Issue: _remote_debugging: No frame limit in get_async_stack_trace() #153364

[maurycy]

Does it actually need to be recursive?

To put aside recursive v. iterative; CS101 strikes: if you ask me, I was thinking about a visited set here... not applicable to this fix but cycle detected would be such a nice touch. :-)

[maurycy]

I realized we used Floyd's algo at least once:

cpython/Python/errors.c

Line 210 in 0c6422f

PyObject *slow_o = o; /* Floyd's cycle detection algo */

I, for one, like Brent's :-)

[maurycy]

Similar recursive problem here:

cpython/Modules/_remote_debugging/asyncio.c

Line 662 in a159c68

process_task_and_waiters(

[maurycy]

Wondering:

• https://github.com/python/cpython/actions/runs/29118077663/job/86446371827

0:04:10 load avg: 5.21 mem: 175.8 MiB [282/505/1] test_external_inspection worker non-zero exit code (Exit code 3221225725 (STATUS_STACK_OVERFLOW))

• https://github.com/python/cpython/actions/runs/29118077663/job/86446371829

0:04:10 load avg: 5.21 mem: 175.8 MiB [282/505/1] test_external_inspection worker non-zero exit code (Exit code 3221225725 (STATUS_STACK_OVERFLOW))

On one hand, it hints at iterative approach being the right now. On the other hand, I've just lowered the limit: 353f815 and, eventually, c9f1ebd

[maurycy]

Not the scope but maybe MAX_THREADS, MAX_STACK_CHUNKS, MAX_LINETABLE_ENTRIES or MAX_ITERATIONS are worth keeping here too