runtime/race: Go 1.2 race detector and map of pointers => nil defererence, segfault

[gopherbot]

by andres.erbsen:

This bug does not appear (at least with the same test code) on the development version
(go version devel +93ad232384f8 Fri Apr 11 10:11:21 2014 -0700 linux/amd64) and may
therefore be already fixed.

The combination of go 1.2, the race detector, a map of pointers and a function returning
two values somehow results in a nil dereference on linux/x86_64.

What does 'go version' print?
go version go1.2.1 linux/amd64

What steps reproduce the problem?
If possible, include a link to a program on play.golang.org.

1. Compile http://play.golang.org/p/0fIDCUE2m2c with "-race"
2. Run it

What happened?

panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x0 pc=0x400c52]

goroutine 1 [running]:
runtime.panic(0x438400, 0x4aea68)
    /build/go/src/go-1.2.1/src/pkg/runtime/panic.c:266 +0xb6
main.main()
    main.go:10 +0x52

What should have happened instead?

no output

Either uncommenting the seemingly nop read from the map or compiling without
"-race" makes the segfault not happen.

[gopherbot]

Comment 1 by andres.erbsen:

The playground link seems to be dead:
package main
var f = func() (int, int) {
    return 0, 0
}
var m = map[int]*int{1: new(int)}
func main() {
    // _ = m[1]
    _, *m[1] = f()
}

[davecheney]

Comment 2:

Hello,
This appears to be fixed at tip.
odessa(~/src) % go run -race rr.go
odessa(~/src) % go version
go version devel +8e553855d1a3 Thu Apr 10 21:46:00 2014 -0700 + darwin/amd64
As it is very unlikely that there will be a 1.2.2 release, I'm making this issue fixed
for Go 1.3
Cheers
Dave

Labels changed: added release-go1.3, repo-main, racedetector.

Status changed to Fixed.

[remyoudompheng]

Comment 3:

It looks similar to issue #7561 but appears to be a different issue.

[dvyukov]

Comment 4:

If it's different, why it's fixed on tip?
Do we need to add another test?