From: "soulcutter (Bradley Schaefer) via ruby-core" <ruby-core@...>
Date: 2025-07-11T16:13:16+00:00
Subject: [ruby-core:122730] [Ruby Bug#18903] Stack overflow signal handling seems to be triggered once and then not working after

Issue #18903 has been updated by soulcutter (Bradley Schaefer).


One observation I have is that there are ways to prevent this in application code:

```ruby
require 'json'
circular_reference_hash = {}.tap { |h| h[:self] = h }

# Globally
JSON.dump_default_options[:max_nesting] = 100
JSON.dump(circular_reference_hash)

# More-specifically
#   JSON.dump(obj, io = nil, limit = nil)
Dumps obj as a JSON string, i.e. 
JSON.dump(circular_reference_hash, nil, 100)
```

I picked `100`, because that happens to be the default `max_nesting` option in `JSON.generate` (and also `to_json`, which uses the same defaults). I guess I'm wondering why `dump` has unsafe defaults in comparison to `generate` - maybe dump's defaults could match generate's (at least for `max_nesting`)?


----------------------------------------
Bug #18903: Stack overflow signal handling seems to be triggered once and then not working after
https://bugs.ruby-lang.org/issues/18903#change-114011

* Author: chrisseaton (Chris Seaton)
* Status: Open
* ruby -v: ruby 3.1.2p20 (2022-04-12 revision 4491bb740a) [arm64-darwin21]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
This program creates a recursive object graph and then tries to convert it to JSON with no max depth, so it stack overflows in C code that does no co-operative stack overflow checks, as the bytecode interpreter would. This therefore triggers a segmentation fault and the stack overflow detection there. It works the first time, but the second time around it doesn't and the program hard crashes on M1.

Is there something like a guard page permission that is switched during the handling, and needs to switched back for the guard page to work again?

Note that it isn't JSON specific - I think any stack overflow within C code would do it.

```ruby
require 'json'

a = []
a << a

begin
  JSON.dump(a)
rescue Exception
  puts 'rescued'
end

JSON.dump(a)
```



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