With sendfile() in threads ("aio threads; sendfile on;"), client connection can block on writing, waiting for sendfile() to complete. In HTTP/2 this might result in the request hang, since an attempt to continue processing in thread event handler will call request's write event handler, which is usually stopped by ngx_http_v2_send_chain(): it does nothing if there are no additional data and stream->queued is set. Further, HTTP/2 resets stream's c->write->ready to 0 if writing blocks, so just fixing ngx_http_v2_send_chain() is not enough.
The following tests currently fail: h2_keepalive.t, h2_priority.t, h2_proxy_max_temp_file_size.t, h2.t, h2_trailers.t.
Similarly, sendfile() with AIO preloading on FreeBSD can block as well, with similar results. This is, however, harder to reproduce, especially on modern FreeBSD systems, since sendfile() usually does not return EBUSY.
Fix is to modify ngx_http_v2_send_chain() so it actually tries to send data to the main connection when called, and to make sure that c->write->ready is set by the relevant event handlers.show more ...