From: "luke-gru (Luke Gruber) via ruby-core" <ruby-core@...>
Date: 2023-02-01T13:38:13+00:00
Subject: [ruby-core:112170] [Ruby master Bug#19395] Process forking within non-main Ractor causes segv

Issue #19395 has been updated by luke-gru (Luke Gruber).

ruby -v set to 3.2.0

Ubuntu 22.04, the issue seems to be calling `rb_native_mutex_destroy` on a locked mutex in `ractor_free`.

Relevant part of the backtrace:

```
/home/lukeg/.rbenv/versions/3.2.0/lib/libruby.so.3.2(die+0x0) [0x7fc1374d0e5f] /tmp/ruby-build.20230103230257.28392.jU9iPR/ruby-3.2.0/error.c:798

/home/lukeg/.rbenv/versions/3.2.0/lib/libruby.so.3.2(rb_bug) /tmp/ruby-build.20230103230257.28392.jU9iPR/ruby-3.2.0/error.c:800

/home/lukeg/.rbenv/versions/3.2.0/lib/libruby.so.3.2(rb_bug_errno+0x43) [0x7fc137579223] /tmp/ruby-build.20230103230257.28392.jU9iPR/ruby-3.2.0/error.c:829

/home/lukeg/.rbenv/versions/3.2.0/lib/libruby.so.3.2(rb_native_mutex_destroy+0x24) [0x7fc137719a24] /tmp/ruby-build.20230103230257.28392.jU9iPR/ruby-3.2.0/thread_pthread.c:603

/home/lukeg/.rbenv/versions/3.2.0/lib/libruby.so.3.2(ractor_free+0x11) [0x7fc137679991] /tmp/ruby-build.20230103230257.28392.jU9iPR/ruby-3.2.0/ractor.c:235

/home/lukeg/.rbenv/versions/3.2.0/lib/libruby.so.3.2(run_final+0xf) 
```

If instead you change `exit 0` to `exec "date"`, it doesn't crash. Maybe the atfork hooks need to be changed to acquire locks in parent, unlock in child.

----------------------------------------
Bug #19395: Process forking within non-main Ractor causes segv
https://bugs.ruby-lang.org/issues/19395#change-101606

* Author: luke-gru (Luke Gruber)
* Status: Feedback
* Priority: Normal
* ruby -v: 3.2.0
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
```ruby
def test_fork_in_ractor
  r2 = Ractor.new do
    pid = fork do
      exit Ractor.count
    end
    pid
  end
  pid = r2.take
  puts "Process #{Process.pid} waiting for #{pid}"
  _pid, status = Process.waitpid2(pid) # stuck forever
  if status.exitstatus != 1
    raise "status is #{status.exitstatus}"
  end
end
test_fork_in_ractor()
 ```

$ top # shows CPU usage is high for child process



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