ThreadSanitizer says:

WARNING: DATA RACE at 0x000040119588
Read by goroutine 152:
  net/http.(*bodyEOFSignal).Close()
      src/pkg/net/http/transport.go:813 +0x41
  net/http.(*persistConn).readLoop()
      src/pkg/net/http/transport.go:558 +0x3f2
Previous write by goroutine 30:
  net/http.(*bodyEOFSignal).Close()
      src/pkg/net/http/transport.go:816 +0x78
  net/http_test.func·097()
      src/pkg/net/http/transport_test.go:894 +0x499
Goroutine 152 (running) created at:
  net/http.(*Transport).getConn()
      src/pkg/net/http/transport.go:390 +0x7be
  net/http.(*Transport).RoundTrip()
      src/pkg/net/http/transport.go:156 +0x31e
  net/http.send()
      src/pkg/net/http/client.go:141 +0x47c
  net/http.(*Client).doFollowingRedirects()
      src/pkg/net/http/client.go:254 +0x941
  net/http.(*Client).Get()
      src/pkg/net/http/client.go:201 +0xc1
  net/http_test.func·097()
      src/pkg/net/http/transport_test.go:878 +0xec
Goroutine 30 (running) created at:
  net/http_test.TestTransportConcurrency()
      src/pkg/net/http/transport_test.go:896 +0x2be
  testing.tRunner()
      src/pkg/testing/testing.go:279 +0x86

13810:c793f0042883 (Jul 24 tip)