ruby · luke-gruber · Jul 7, 2025
diff --git a/process.c b/process.c
@@ -4010,6 +4010,7 @@ retry_fork_async_signal_safe(struct rb_process_status *status, int *ep,
 
     while (1) {
         prefork();
+        rb_thread_acquire_fork_lock();
         disable_child_handler_before_fork(&old);
 #ifdef HAVE_WORKING_VFORK
         if (!has_privilege())
@@ -4036,6 +4037,7 @@ retry_fork_async_signal_safe(struct rb_process_status *status, int *ep,
         }
         err = errno;
         disable_child_handler_fork_parent(&old);
+        rb_thread_release_fork_lock();
         if (0 < pid) /* fork succeed, parent process */
             return pid;
         /* fork failed */

diff --git a/test/ruby/test_process.rb b/test/ruby/test_process.rb
@@ -2852,4 +2852,22 @@ def test_handle_interrupt_with_fork
   rescue RuntimeError
     # Ignore.
   end if defined?(fork)
+
+  def test_concurrent_kernel_system_with_ractors_does_not_crash
+    omit "system('ls') is not supported" if windows?
+    assert_ractor <<-RUBY
+      rs = []
+      100.times do
+        rs << Ractor.new do
+          # system uses fork() internally, so does IO.popen and Process.spawn.
+          system("ls > /dev/null")
+        end
+      end
+
+      while rs.any?
+        r, _obj = Ractor.select(*rs)
+        rs.delete(r)
+      end
+    RUBY
+  end
 end