internal/poll: data race in (*FD).SetBlocking

[twmb]

What version of Go are you using (go version)?

go version devel +7974f0815e Mon Mar 19 21:51:23 2018 +0000 linux/amd64

This is new in 1.10.

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOCACHE="/home/twmb/.cache/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/twmb/go"
GORACE=""
GOROOT="/home/twmb/go/go"
GOTMPDIR=""
GOTOOLDIR="/home/twmb/go/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build478075614=/tmp/go-build -gno-record-gcc-switches"

What did you do?

For net:
https://play.golang.org/p/p2p0vliZwJB
For os:
https://play.golang.org/p/st7Npi4-2oQ

What did you expect to see?

With go run -race on that file, no leak.

What did you see instead?

==================
WARNING: DATA RACE
Write at 0x00c42013e7af by goroutine 64:
  internal/poll.(*FD).SetBlocking()
      /home/twmb/go/go/src/internal/poll/fd_unix.go:121 +0x8f
  net.(*netFD).dup()
      /home/twmb/go/go/src/net/fd_unix.go:316 +0x7d
  net.(*conn).File()
      /home/twmb/go/go/src/net/net.go:294 +0x4d
  main.main.func2()
      /home/twmb/testing/junk.go:29 +0x3a

Previous write at 0x00c42013e7af by goroutine 66:
  internal/poll.(*FD).SetBlocking()
      /home/twmb/go/go/src/internal/poll/fd_unix.go:121 +0x8f
  net.(*netFD).dup()
      /home/twmb/go/go/src/net/fd_unix.go:316 +0x7d
  net.(*conn).File()
      /home/twmb/go/go/src/net/net.go:294 +0x4d
  main.main.func3()
      /home/twmb/testing/junk.go:34 +0x3a

Goroutine 64 (running) created at:
  main.main()
      /home/twmb/testing/junk.go:28 +0x13f

Goroutine 66 (running) created at:
  main.main()
      /home/twmb/testing/junk.go:33 +0x161
==================

For os:

starting
==================
WARNING: DATA RACE
Write at 0x00c42009416f by goroutine 10:
  internal/poll.(*FD).SetBlocking()
      /home/twmb/go/go/src/internal/poll/fd_unix.go:121 +0x8f
  os.(*File).Fd()
      /home/twmb/go/go/src/os/file_unix.go:69 +0xce

Previous write at 0x00c42009416f by goroutine 11:
  internal/poll.(*FD).SetBlocking()
      /home/twmb/go/go/src/internal/poll/fd_unix.go:121 +0x8f
  os.(*File).Fd()
      /home/twmb/go/go/src/os/file_unix.go:69 +0xce

Goroutine 10 (running) created at:
  main.main()
      /home/twmb/testing/junk.go:18 +0xa3

Goroutine 11 (finished) created at:
  main.main()
      /home/twmb/testing/junk.go:19 +0xc5
==================
done

0f3ab149ec4 introduced SetBlocking on file descriptors that can be pollable. SetBlocking sets isBlocking in a struct. SetBlocking is not called often, but the call itself is unprotected when it is. Documentation does not suggest that the calls themselves should be protected.

[bcmills]

(CC @ianlancetaylor)

[ianlancetaylor]

I believe the fix mentioned in #24483 would fix this one too. I am still skeptical as to whether this is a problem that real programs will encounter.

[ianlancetaylor]

This data race in the net package was removed as a side-effect of fixing #24942.

[gopherbot]

Change https://golang.org/cl/119955 mentions this issue: os, net: avoid races between dup, set-blocking-mode, and closing

[gopherbot]

Change https://golang.org/cl/123176 mentions this issue: internal/poll: don't take read lock in SetBlocking