runtime: poor error message for Goexit on C-created thread #68275
Description
Go version
tip
Output of go env in your module/workspace:
N/AWhat did you do?
// Copyright 2024 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
/*
#include <pthread.h>
void go_callback();
static void *thr(void *arg) {
go_callback();
return 0;
}
static void foo() {
pthread_t th;
pthread_attr_t attr;
pthread_attr_init(&attr);
pthread_attr_setstacksize(&attr, 256 << 10);
pthread_create(&th, &attr, thr, 0);
pthread_join(th, 0);
}
*/
import "C"
import (
"runtime"
)
//export go_callback
func go_callback() {
runtime.Goexit()
}
func main() {
C.foo()
}What did you see happen?
runtime: mp.lockedInt = 1
fatal error: exited a goroutine internally locked to the OS thread
runtime stack:
runtime.throw({0x4851c4?, 0x600000000?})
/usr/lib/google-golang/src/runtime/panic.go:1069 +0x48 fp=0x7fe3895c5dd0 sp=0x7fe3895c5da0 pc=0x460028
runtime.gdestroy(0xc000006700)
/usr/lib/google-golang/src/runtime/proc.go:4324 +0x2a5 fp=0x7fe3895c5e10 sp=0x7fe3895c5dd0 pc=0x43bc85
runtime.goexit0(0xc000006700?)
/usr/lib/google-golang/src/runtime/proc.go:4278 +0x13 fp=0x7fe3895c5e28 sp=0x7fe3895c5e10 pc=0x43b9b3
runtime.mcall()
/usr/lib/google-golang/src/runtime/asm_amd64.s:459 +0x4e fp=0x7fe3895c5e40 sp=0x7fe3895c5e28 pc=0x46450e
goroutine 1 gp=0xc0000061c0 m=0 mp=0x4fcf20 [syscall]:
runtime.cgocall(0x46ab00, 0xc000058740)
/usr/lib/google-golang/src/runtime/cgocall.go:167 +0x4b fp=0xc000058718 sp=0xc0000586e0 pc=0x45d60b
main._Cfunc_foo()
_cgo_gotypes.go:43 +0x3f fp=0xc000058740 sp=0xc000058718 pc=0x46aa3f
main.main()
/tmp/c/main.go:38 +0xf fp=0xc000058750 sp=0xc000058740 pc=0x46aa6f
runtime.main()
/usr/lib/google-golang/src/runtime/proc.go:272 +0x28b fp=0xc0000587e0 sp=0xc000058750 pc=0x4337eb
runtime.goexit({})
/usr/lib/google-golang/src/runtime/asm_amd64.s:1700 +0x1 fp=0xc0000587e8 sp=0xc0000587e0 pc=0x4664e1
Note that this error was improved a bit recently in https://go.dev/cl/583675. In 1.22, the error is
invalid m->lockedInt = 1
fatal error: internal lockOSThread error
runtime stack:
...
What did you expect to see?
A more clear description of the problem.
The problem here is that it is not valid to call runtime.Goexit in a cgo callback from C to Go on a C-created thread. I think that restriction is fine (it is unclear what Goexit should do if we were to allow it), but the error message here should be more clear.
I think with an additional mp.isextra check in gdestroy we could be more explicit about what the user did wrong.
We should also update the runtime.Goexit docs to mention this case.