runtime: go1.8.rc1 GC crash with MakeFunc #18635
Description
What version of Go are you using (go version)?
go version go1.8rc1 linux/amd64
What operating system and processor architecture are you using (go env)?
# go env
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/opt/go/"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build572059213=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
What did you do?
We very much need the improvements in go1.8, and so have been building and testing with the go1.8rc1. I was seeing panics during "copystack". After considerable effort I was able to reduce the problem code to this somewhat contrived example:
package main
import (
"log"
"reflect"
)
func main() {
go func() {
sum := 0
for {
garbage := make([]byte, 1, 10*1024*1024)
sum += int(garbage[0])
}
}()
// Build runnable function creator
ret := func() reflect.Value {
newfun := func(in []reflect.Value) []reflect.Value {
return reflect.ValueOf(Max).Call([]reflect.Value{})
}
outType := reflect.FuncOf([]reflect.Type{}, []reflect.Type{}, false)
return reflect.MakeFunc(outType, newfun)
}
NextFn = func() interface{} { return ret().Interface() }
// Run function recursively
NextFn().(func())()
}
var NextFn func() interface{}
var ProgramStateDepth = 0
func Max() {
ProgramStateDepth++
log.Println("Depth", ProgramStateDepth)
next := NextFn().(func())
next()
}
This actually produces the same panic, but it happens during gc. On my machine it may take anywhere from 2 to 10000 "iterations" of Max, but it always crashes within seconds. Here is the output in a run where it crashed after 1 iteration:
2017/01/12 17:23:08 Depth 1
runtime: confused by reflect.makeFuncStub
fatal error: reflect mismatch
runtime stack:
runtime.throw(0x4d1c7b, 0x10)
/usr/local/go/src/runtime/panic.go:596 +0x95
runtime.getArgInfo(0xc420037c00, 0x522a70, 0xc420037a01, 0x0, 0x10, 0x0)
/usr/local/go/src/runtime/traceback.go:589 +0x177
runtime.gentraceback(0xffffffffffffffff, 0xc420a911a0, 0x0, 0xc4200001a0, 0x0, 0x0, 0x7fffffff, 0xc420037df0, 0x0, 0x0, ...)
/usr/local/go/src/runtime/traceback.go:342 +0x117b
runtime.scanstack(0xc4200001a0, 0xc42001d228)
/usr/local/go/src/runtime/mgcmark.go:842 +0x265
runtime.scang(0xc4200001a0, 0xc42001d228)
/usr/local/go/src/runtime/proc.go:866 +0x209
runtime.markroot.func1()
/usr/local/go/src/runtime/mgcmark.go:264 +0x6d
runtime.systemstack(0xc420037f28)
/usr/local/go/src/runtime/asm_amd64.s:343 +0xab
runtime.markroot(0xc42001d228, 0x5)
/usr/local/go/src/runtime/mgcmark.go:269 +0x1e2
runtime.gcDrain(0xc42001d228, 0x5)
/usr/local/go/src/runtime/mgcmark.go:1051 +0xbe
runtime.gcBgMarkWorker.func2()
/usr/local/go/src/runtime/mgc.go:1522 +0xe0
runtime.systemstack(0xc42001c000)
/usr/local/go/src/runtime/asm_amd64.s:327 +0x79
runtime.mstart()
/usr/local/go/src/runtime/proc.go:1132
goroutine 4 [GC worker (idle)]:
runtime.systemstack_switch()
/usr/local/go/src/runtime/asm_amd64.s:281 fp=0xc420027750 sp=0xc420027748
runtime.gcBgMarkWorker(0xc42001c000)
/usr/local/go/src/runtime/mgc.go:1527 +0x1fc fp=0xc4200277d8 sp=0xc420027750
runtime.goexit()
/usr/local/go/src/runtime/asm_amd64.s:2197 +0x1 fp=0xc4200277e0 sp=0xc4200277d8
created by runtime.gcBgMarkStartWorkers
/usr/local/go/src/runtime/mgc.go:1402 +0x98
goroutine 1 [runnable (scan)]:
fmt.(*pp).printArg(0xc42004c000, 0x4b1580, 0xc42000e128, 0xc400000076)
/usr/local/go/src/fmt/print.go:604 +0xa37
fmt.(*pp).doPrintln(0xc42004c000, 0xc420a912e8, 0x2, 0x2)
/usr/local/go/src/fmt/print.go:1138 +0xa1
fmt.Sprintln(0xc420a912e8, 0x2, 0x2, 0xc42000e128, 0x553398)
/usr/local/go/src/fmt/print.go:264 +0x56
log.Println(0xc420a912e8, 0x2, 0x2)
/usr/local/go/src/log/log.go:297 +0x3f
main.Max()
/tmp/crash/crash.go:35 +0xe9
reflect.Value.call(0x4b0340, 0x4d7588, 0x13, 0x4d0495, 0x4, 0xc420a91740, 0x0, 0x0, 0x1c, 0x4b0340, ...)
/usr/local/go/src/reflect/value.go:434 +0x91f
reflect.Value.Call(0x4b0340, 0x4d7588, 0x13, 0xc420a91740, 0x0, 0x0, 0xc42006e100, 0x20, 0x20)
/usr/local/go/src/reflect/value.go:302 +0xa4
main.main.func2.1(0x553500, 0x0, 0x0, 0x553500, 0x0, 0x0)
/tmp/crash/crash.go:20 +0x7b
reflect.callReflect(0xc42006e100, 0xc420a91908)
/usr/local/go/src/reflect/value.go:508 +0x38f
reflect.makeFuncStub(0x4b0340, 0xc42006e100, 0x2, 0xc4200581c0, 0x4d05eb, 0x5, 0x4b1ac0, 0xc420058140, 0x4b1580, 0xc4200581c0, ...)
/usr/local/go/src/reflect/asm_amd64.s:17 +0x40
main.Max()
/tmp/crash/crash.go:37 +0x10f
reflect.Value.call(0x4b0340, 0x4d7588, 0x13, 0x4d0495, 0x4, 0xc42003bd90, 0x0, 0x0, 0xc42005c0f0, 0x4b0340, ...)
/usr/local/go/src/reflect/value.go:434 +0x91f
reflect.Value.Call(0x4b0340, 0x4d7588, 0x13, 0xc42003bd90, 0x0, 0x0, 0xc42006e0e0, 0x20, 0x20)
/usr/local/go/src/reflect/value.go:302 +0xa4
main.main.func2.1(0x553500, 0x0, 0x0, 0x553500, 0x0, 0x0)
/tmp/crash/crash.go:20 +0x7b
reflect.callReflect(0xc42006e0e0, 0xc420a91f58)
/usr/local/go/src/reflect/value.go:508 +0x38f
reflect.makeFuncStub(0x4b0340, 0xc42006e0e0, 0xc4200001a0, 0xc4200581a0, 0xc420a91fd0, 0x42802a, 0xc420056000, 0x0, 0xc420056000, 0x0, ...)
/usr/local/go/src/reflect/asm_amd64.s:17 +0x40
main.main()
/tmp/crash/crash.go:27 +0xaf
goroutine 18 [GC assist wait]:
main.main.func1()
/tmp/crash/crash.go:12 +0x3f
created by main.main
/tmp/crash/crash.go:15 +0x39
As with the stack crash, the key seems to be:
runtime: confused by reflect.makeFuncStub
fatal error: reflect mismatch
BTW - go1.8 performance is amazing - Thanks!