Upstream: reading from a client after connection upgrade. Read event on a client connection might have been disabled during previous processing, and we at least need to handle events. Calling ngx_http_upstream_process_upgraded() is a simpliest way to do it. Notably this change is needed for select, poll and /dev/poll event methods. Previous version of this patch was posted here: http://mailman.nginx.org/pipermail/nginx/2014-January/041839.html