From: "wanabe (_ wanabe) via ruby-core" <ruby-core@...>
Date: 2023-10-12T12:56:38+00:00
Subject: [ruby-core:115018] [Ruby master Bug#19922] ObjectSpace.dump_all in multiple threads in parallel causes SEGV

Issue #19922 has been reported by wanabe (_ wanabe).

----------------------------------------
Bug #19922: ObjectSpace.dump_all in multiple threads in parallel causes SEGV
https://bugs.ruby-lang.org/issues/19922

* Author: wanabe (_ wanabe)
* Status: Open
* Priority: Normal
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
`ObjectSpace.dump_all` in multiple threads in parallel causes SEGV.
The reproduce code is here:
```
$ ruby -robjspace -e 'def dump; 10.times { ObjectSpace.dump_all } end; Thread.new { dump }; dump'
/home/wanabe/.rbenv/versions/master/lib/ruby/3.3.0+0/objspace.rb:100: [BUG] Segmentation fault at 0x0000000000000000
(snip)
```

I attached the full log.

I assumed that:
- Thread1
  - calls `rb_objspace_reachable_objects_from_root()`
  - changes `GET_RACTOR()->mfd`: mfd1
  - calls `dump_flush()`
    - changes current thread due to IO
- Thread2
  - calls `rb_objspace_reachable_objects_from_root()`
  - changes `GET_RACTOR()->mfd`: mfd2
  - calls `dump_flush()`
    - changes current thread due to IO
- Thread1
  - gets unexpected `GET_RACTOR()->mfd`: mfd2

---Files--------------------------------
bug.log (23.1 KB)


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