I've added instrumentation to syscall.Sendfile(), so that it synchronizes with
syscall.Read(), but race builder still shows a race.
It's either another bug in race detector, or bug in the test.
What is strange is that race detector detector says that fd.close() happened before
Sendfile() according to wall clock time. It means that something really weird happens in
the test.


http://build.golang.org/log/bf2017abd5123b784f65272a7cc3eb8f1ccf3e13

WARNING: DATA RACE
Read by goroutine 142:
  net.sendFile()
      /usr/local/go/src/pkg/net/sendfile_linux.go:47 +0x5da
  net.(*TCPConn).ReadFrom()
      /usr/local/go/src/pkg/net/tcpsock_posix.go:80 +0x49
  net/http.(*response).ReadFrom()
      /usr/local/go/src/pkg/net/http/server.go:161 +0x11c
  io.CopyN()
      /usr/local/go/src/pkg/io/io.go:305 +0x1a0
  net/http.serveContent()
      /usr/local/go/src/pkg/net/http/fs.go:236 +0xaa0
  net/http.ServeContent()
      /usr/local/go/src/pkg/net/http/fs.go:118 +0x184
  net/http_test.func·024()
      /usr/local/go/src/pkg/net/http/fs_test.go:551 +0x19f
  ??()
      -:0 +0x401038a1
  net/http/httptest.(*waitGroupHandler).ServeHTTP()
      /usr/local/go/src/pkg/net/http/httptest/server.go:180 +0xcb
  net/http.(*conn).serve()
      /usr/local/go/src/pkg/net/http/server.go:681 +0x7a7

Previous write by goroutine 15:
  os.(*file).close()
      /usr/local/go/src/pkg/os/file_unix.go:110 +0x15e
  os.(*File).Close()
      /usr/local/go/src/pkg/os/file_unix.go:99 +0x43
  net/http_test.TestServeContent()
      /usr/local/go/src/pkg/net/http/fs_test.go:626 +0x1710
  testing.tRunner()
      /usr/local/go/src/pkg/testing/testing.go:301 +0x8f

Goroutine 142 (running) created at:
  net/http.(*Server).Serve()
      /usr/local/go/src/pkg/net/http/server.go:1116 +0x45e

Goroutine 15 (running) created at:
  testing.RunTests()
      /usr/local/go/src/pkg/testing/testing.go:377 +0xa8b
  testing.Main()
      /usr/local/go/src/pkg/testing/testing.go:313 +0xcd
  main.main()
      net/http/_test/_testmain.go:301 +0xda
  runtime.main()
      /usr/local/go/src/pkg/runtime/proc.c:248 +0x91