Bug #21610: Use ec->interrupt_mask to prevent interrupts.

• Status: Closed
• Assignee: ioquatix (Samuel Williams)
• Target version: -
• Backport: 3.2: REQUIRED, 3.3: REQUIRED, 3.4: DONE

[ioquatix (Samuel Williams)]

The following program can trigger rb_bug in rb_fiber_scheduler_unblock:

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

[ioquatix (Samuel Williams)]

• Assignee set to ioquatix (Samuel Williams)
• Backport changed from 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN to 3.2: REQUIRED, 3.3: REQUIRED, 3.4: REQUIRED

[ioquatix (Samuel Williams)]

• Status changed from Open to Closed

Fixed in https://github.com/ruby/ruby/commit/e6879401feba22e3657a231cbedc751998cb7176

[ioquatix (Samuel Williams)]

A slightly different change may be required for 3.3 and 3.2 backports: https://github.com/ruby/ruby/commit/e900e9fc9ace5e36de5170c83df0f56167e4c8a9

[ioquatix (Samuel Williams)]

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