runtime: Invalid "concurrent map writes" after recovered runtime-panic on previous map assign with non-comparable key

[navytux]

Please answer these questions before submitting your issue. Thanks!

What did you do?

Please consider the following program:

package main

import "fmt"

// mapSet sets m[key] = value, but returns error when k is of not-appropriate type
func mapSet(m map[interface{}]interface{}, key, value interface{}) (err error) {
        defer func() {
                if r := recover(); r != nil {
                        // XXX it is better to check r.Error() to has "unhashable type ..."
                        err = fmt.Errorf("mapSet: %v", r)
                }
        }()

        m[key] = value
        return nil

}

func main() {
        m := make(map[interface{}]interface{})
        //keyv := []interface{} {"aaa", "hello"}
        keyv := []interface{} {[]int{1, 2, 3}, "hello"}
        v := "world"

        for i, k := range keyv {
                err := mapSet(m, k, v)
                fmt.Printf("step%d: key = %#v -> %v\n", i, k, err)
        }
}

(https://play.golang.org/p/_YPsKUivic)

What did you expect to see?

step0: key = []int{1, 2, 3} -> mapSet: runtime error: hash of unhashable type []int
step1: key = "hello" -> <nil>

What did you see instead?

step0: key = []int{1, 2, 3} -> mapSet: runtime error: hash of unhashable type []int
fatal error: concurrent map writes

goroutine 1 [running]:
runtime.throw(0x4aaf32, 0x15)
        /home/kirr/src/tools/go/go/src/runtime/panic.go:596 +0x95 fp=0xc42003bc60 sp=0xc42003bc40
runtime.mapassign(0x4928e0, 0xc42003be08, 0xc42003bd20, 0x1)
        /home/kirr/src/tools/go/go/src/runtime/hashmap.go:499 +0x688 fp=0xc42003bd00 sp=0xc42003bc60
main.mapSet(0xc42003be08, 0x48d240, 0x4b3120, 0x48d240, 0xc42000e310, 0x0, 0x0)
        /home/kirr/tmp/trashme/mapassign.go:14 +0x9e fp=0xc42003bd40 sp=0xc42003bd00
main.main()
        /home/kirr/tmp/trashme/mapassign.go:26 +0x217 fp=0xc42003bf88 sp=0xc42003bd40
runtime.main()
        /home/kirr/src/tools/go/go/src/runtime/proc.go:185 +0x20a fp=0xc42003bfe0 sp=0xc42003bf88
runtime.goexit()
        /home/kirr/src/tools/go/go/src/runtime/asm_amd64.s:2148 +0x1 fp=0xc42003bfe8 sp=0xc42003bfe0
exit status 2

Does this issue reproduce with the latest release (go1.8)?

yes

System details

go version devel +f072283bce Thu Mar 2 06:08:42 2017 +0000 linux/amd64
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/kirr/go"
GORACE=""
GOROOT="/home/kirr/src/tools/go/go"
GOTOOLDIR="/home/kirr/src/tools/go/go/pkg/tool/linux_amd64"
GCCGO="/usr/bin/gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build846511103=/tmp/go-build -gno-record-gcc-switches"
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"
GOROOT/bin/go version: go version devel +f072283bce Thu Mar 2 06:08:42 2017 +0000 linux/amd64
GOROOT/bin/go tool compile -V: compile version devel +f072283bce Thu Mar 2 06:08:42 2017 +0000 X:framepointer
uname -sr: Linux 4.9.0-1-amd64
Distributor ID:	Debian
Description:	Debian GNU/Linux 9.0 (stretch)
Release:	9.0
Codename:	stretch
/lib/x86_64-linux-gnu/libc.so.6: GNU C Library (Debian GLIBC 2.24-9) stable release version 2.24, by Roland McGrath et al.
gdb --version: GNU gdb (Debian 7.12-6) 7.12.0.20161007-git

---

The question here is whether map should be still considered usable after access with non-comparable element.

This issue originally came in the context of decoding python pickles and what to use - panics or reflect to detect non-comparable dict keys:

kisielk/og-rek#30 (comment) (and below).

Thanks beforehand,
Kirill

[gopherbot]

CL https://golang.org/cl/37665 mentions this issue.

[navytux]

Thanks for fixing.