post <- builder ~ `^plan9` && pkg == "net/http" && test == "TestServerWriteTimeout"
As of CL 449935, the plan9-amd64-0intro builder went from failing something like 25% of the time to failing nearly 100% of the time.
The vast majority of the current failures are test timeouts running net/http, and they all seem to involve goroutines parked in net/http.(*http2ClientConn).RoundTrip via net/http_test.testServerWriteTimeout.
I think this is probably because the plan9 netpoll implementation does not support (or does not fully support?) SetDeadline.