ruby - Stack level too deep error after running bundle update -

i have rails app run fine months. however, yesterday, after i've run bundle update, cannot start server anymore. whenever start webrick raises error:

.rvm/gems/ruby-1.9.3-p392/gems/rack-1.4.5/lib/rack/builder.rb:40: stack level deep (systemstackerror) 

i don't know cause base on above error message.

also gemfile: gemfile

can me solve problem

only thing occurs me @ moment rollback app running , try update 1 gem @ time. way find 1 causing issue , may there.