load.c: avoid segfault when 'throw' occurs in the middle of rb_load_file_str

How can a 'throw' happen while the current thread is reading a Ruby source file
from disk and parsing it? It can happen if another thread calls Thread#raise,
and passes an Exception object which responds to #exception, and the custom #exception
method calls Kernel#throw.

In practice, this is most likely to happen if you combine the use of autoload and
Timeout.timeout.

An extra check is required to avoid a segfault in this case.

* load.c (rb_load_internal0): extra check before returning TAG_RAISE when a
  non-local transfer of control happens while loading and parsing a Ruby source file.
  [ruby-core:70169] [Bug #11404]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@51439 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,10 @@
+Thu Jul 30 10:42:27 2015  Alex Dowad  <alexinbeijing@gmail.com>
+
+	* load.c (rb_load_internal0): extra check before returning
+	  TAG_RAISE when a non-local transfer of control happens while
+	  loading and parsing a Ruby source file.
+	  [ruby-core:70169] [Bug #11404]
+
 Thu Jul 30 08:48:42 2015  Eric Wong  <e@80x24.org>
 
 	* st.c (find_entry): constify st_table*

load.c

@@ -621,7 +621,7 @@ rb_load_internal0(rb_thread_t *th, VALUE fname, int wrap)
     th->top_self = self;
     th->top_wrapper = wrapper;
 
-    if (!loaded && !FIXNUM_P(th->errinfo)) {
+    if (!loaded && !FIXNUM_P(th->errinfo) && state != TAG_THROW) {
 	/* an error on loading don't include INT2FIX(TAG_FATAL) see r35625 */
 	return TAG_RAISE;
     }

test/ruby/test_require.rb

@@ -706,4 +706,33 @@ class TestRequire < Test::Unit::TestCase
       END
     }
   end unless /mswin|mingw/ =~ RUBY_PLATFORM
+
+  def test_throw_while_loading
+    Tempfile.create(%w'bug-11404 .rb') do |f|
+      f.puts 'sleep'
+      f.close
+
+      assert_separately(["-", f.path], <<-'end;')
+        path = ARGV[0]
+        class Error < RuntimeError
+          def exception(*)
+            begin
+              throw :blah
+            rescue UncaughtThrowError
+            end
+            self
+          end
+        end
+
+        assert_throw(:blah) do
+          x = Thread.current
+          y = Thread.start {
+            sleep 0.00001
+            x.raise Error.new
+          }
+          load path
+        end
+      end;
+    end
+  end
 end