From: "nagachika (Tomoyuki Chikanaga) via ruby-core" <ruby-core@...>
Date: 2025-10-05T22:52:20+00:00
Subject: [ruby-core:123400] [Ruby Bug#21610] Use ec->interrupt_mask to prevent interrupts.

Issue #21610 has been updated by nagachika (Tomoyuki Chikanaga).

Backport changed from 3.2: REQUIRED, 3.3: REQUIRED, 3.4: DONE to 3.2: REQUIRED, 3.3: DONE, 3.4: DONE

Thank you for the PRs. Merged into ruby_3_3 at https://github.com/ruby/ruby/commit/183e2b0a2389579a3a5b205113db72345b52dd85.

----------------------------------------
Bug #21610: Use ec->interrupt_mask to prevent interrupts.
https://bugs.ruby-lang.org/issues/21610#change-114770

* Author: ioquatix (Samuel Williams)
* Status: Closed
* Assignee: ioquatix (Samuel Williams)
* Backport: 3.2: REQUIRED, 3.3: DONE, 3.4: DONE
----------------------------------------
The following program can trigger `rb_bug` in `rb_fiber_scheduler_unblock`:

```ruby
require 'async/scheduler'

scheduler = Async::Scheduler.new
Fiber.set_scheduler(scheduler)

Signal.trap(:USR1) do
end

q = Thread::Queue.new

Thread.new do
  loop do
    Ractor.new do
      Process.kill(:USR1, $$)
    end.join
  end
end

Fiber.schedule do
  Fiber.schedule do
    1.upto(1000000) do |i|
      sleep 0.01
      q.pop
      q.push(1)
      puts "1 iter push/pop"
    end
  end
  Fiber.schedule do
    1.upto(1000000) do |i|
      sleep 0.01
      q.push(i)
      q.pop
      puts "1 iter push/pop#2"
    end
  end
  Fiber.schedule do
    gets
    exit!
  end
end
```

In brief, when `rb_fiber_scheduler_unblock` executes with `ec->interrupt_flag` set, the following sequence can occur:

```
Thread A (Signaling)              Thread B (Blocked Fiber)
--------------------              ---------------------
calls unblock(fiber_x)           
������ enters scheduler user code     fiber_x sleeping in scheduler.block()
������ ������  SIGNAL INTERRUPT ������       
������ raises SignalException        
������ unblock operation aborted     
������ scheduler state inconsistent   
������ returns believing success      ������ fiber_x waits forever ������
```

Confirmed fix: https://github.com/ruby/ruby/pull/14588



-- 
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