thread.c: disable VM events when stack overflow

* thread.c (ruby_thread_stack_overflow): disable VM events when
  stack overflow occurred; it causes another stack overflow again
  in making backtrace object, and crashes.
  [ruby-core:80662] [Bug #13425]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58334 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_trace.rb

@@ -59,4 +59,19 @@ class TestTrace < Test::Unit::TestCase
              a.any? {true}
            }.value, bug2722)
   end
+
+  def test_trace_stackoverflow
+    assert_normal_exit("#{<<-"begin;"}\n#{<<~"end;"}")
+    begin;
+      require 'tracer'
+      class HogeError < StandardError
+        def to_s
+          message.upcase        # disable tailcall optimization
+        end
+      end
+      Tracer.stdout = open(IO::NULL, "w")
+      Tracer.on
+      HogeError.new.to_s
+    end;
+  end
 end

thread.c

@@ -2169,6 +2169,7 @@ NORETURN(void ruby_thread_stack_overflow(rb_thread_t *th));
 void
 ruby_thread_stack_overflow(rb_thread_t *th)
 {
+    ruby_vm_event_flags = 0;
     th->raised_flag = 0;
 #ifdef USE_SIGALTSTACK
     if (!rb_threadptr_during_gc(th)) {