runtime: poor error message for Goexit on C-created thread

[prattmic]

Go version

tip

Output of go env in your module/workspace:

N/A

What 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.

[prattmic]

cc @golang/runtime

[gabyhelp]

Related Issues

• fatal error: exitsyscall: syscall frame is no longer valid #63829 (closed)
• runtime: TestCallbackPanic internal lockOSThread error #47382 (closed)
• runtime: "fatal error: attempt to execute system stack code on user stack" in startTemplateThread #39098 (closed)
• runtime: "runtime: unknown pc" from C abort() #47522 (closed)
• runtime/race: sigsegv when using cgo callbacks with the race detector enabled #10874 (closed)
• runtime: stoplockedm: inconsistent locking #21306 (closed)
• runtime: cgo using programs have a goroutine marked [syscall, locked to thread]; #17384 (closed)
• runtime: error on exit of program on darwin fatal error: exitsyscall: syscall frame is no longer valid #42465 (closed)
• os/exec: fatal error: runtime·unlock: lock count #30594 (closed)
• testing: Example test with runtime.Goexit hangs #41084 (closed)

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[gopherbot]

Change https://go.dev/cl/609296 mentions this issue: runtime: Goexit on C-created thread report more useful error message