From: "wanabe (_ wanabe) via ruby-core" <ruby-core@...>
Date: 2026-07-20T10:35:22+00:00
Subject: [ruby-core:126124] [Ruby Bug#19922] ObjectSpace.dump_all in multiple threads in parallel causes SEGV

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

Status changed from Open to Closed

This issue was fixed in commit `3c63a01295b4219743b3d3e883fd4a4a616960a` and has not recurred since then.
Thank you.

```
$ git checkout 3c63a01295b4219743b3d3e883fd4a4a616960a6; make -j8 exts >/dev/null 2>&1 && ./ruby -v -I .ext/x86_64-linux/ -I .ext/common/ -I ../../lib -I. -robjspace -e 'def dump; 100.times { ObjectSpace.dump_all } end; Thread.new { dump }; dump; p :ok' 2>&1|head -n2
HEAD is now at 3c63a01295 Move responsibility of heap walking into Ruby
ruby 3.4.0dev (2024-09-03T14:05:38Z v3_4_0_preview2~649 3c63a01295) [x86_64-linux]
:ok

$ git checkout 3c63a01295b4219743b3d3e883fd4a4a616960a6~; make -j8 exts >/dev/null 2>&1 && ./ruby -v -I .ext/x86_64-linux/ -I .ext/common/ -I ../../lib -I. -robjspace -e 'def dump; 100.times { ObjectSpace.dump_all } end; Thread.new { dump }; dump; p :ok' 2>&1|head -n2
Previous HEAD position was 3c63a01295 Move responsibility of heap walking into Ruby
HEAD is now at a2243ee48b Implement ALIAS NODE keyword locations
ruby 3.4.0dev (2024-09-03T13:09:08Z v3_4_0_preview2~650 a2243ee48b) [x86_64-linux]
/home/wanabe/work/prog/ruby/ruby/tmp/master/.ext/common/objspace.rb:100: [BUG] Segmentation fault at 0x0000000000000000
```

----------------------------------------
Bug #19922: ObjectSpace.dump_all in multiple threads in parallel causes SEGV
https://bugs.ruby-lang.org/issues/19922#change-118127

* Author: wanabe (_ wanabe)
* Status: Closed
* 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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