merge revision(s) 611e711085c7e3984555a79626d025c8b876eced,a9c5c2d614f30a616970245fef3e7ffc151e2ecf: [Backport #17527]

	Test incorrect behaviour of `rb_io_wait_readable/writable`.

	---
	 test/fiber/test_io.rb | 35 +++++++++++++++++++++++++++++++++++
	 1 file changed, 35 insertions(+)

	Check errno before invoking scheduler in
	 `rb_io_wait_readable/writable`.

	See <https://bugs.ruby-lang.org/issues/17527> for more details.
	---
	 io.c | 66 +++++++++++++++++++++++++++++++++++-------------------------------
	 1 file changed, 35 insertions(+), 31 deletions(-)

1 files changed, 35 insertions, 0 deletions

diff --git a/test/fiber/test_io.rb b/test/fiber/test_io.rb
index f01cc3af1b..fafda7c310 100644
--- a/test/fiber/test_io.rb
+++ b/test/fiber/test_io.rb
@@ -62,4 +62,39 @@ class TestFiberIO < Test::Unit::TestCase
       end
     end.each(&:join)
   end
+
+  def test_epipe_on_read
+    skip "UNIXSocket is not defined!" unless defined?(UNIXSocket)
+
+    i, o = UNIXSocket.pair
+
+    unless i.nonblock? && o.nonblock?
+      i.close
+      o.close
+      skip "I/O is not non-blocking!"
+    end
+
+    error = nil
+
+    thread = Thread.new do
+      scheduler = Scheduler.new
+      Fiber.set_scheduler scheduler
+
+      Fiber.schedule do
+        begin
+          i.close
+          o.write(MESSAGE)
+        rescue => error
+          # Saved into error.
+        end
+      end
+    end
+
+    thread.join
+
+    i.close
+    o.close
+
+    assert_kind_of Errno::EPIPE, error
+  end
 end