if e != 0 {
					return e
				}
				return nil
			},
		},
	}

	waiter := func(q <-chan uintptr, r chan<- uintptr, once bool) {
		for x := range q {
			runtime.LockOSThread()
			v, _, e := syscall.Syscall(syscall.SYS_PRCTL, PR_GET_KEEPCAPS, 0, 0)
			if e != 0 {
				t.Errorf("tid=%d prctl(PR_GET_KEEPCAPS) failed: %v", syscall.Gettid(), e)
			} else if x != v {

// of goroutines. A Go program creates a new thread only when a goroutine
// is ready to run but all the existing threads are blocked in system calls, cgo calls,
// or are locked to other goroutines due to use of runtime.LockOSThread.
//
// SetMaxThreads is useful mainly for limiting the damage done by
// programs that create an unbounded number of threads. The idea is
// to take down the program before it takes down the operating system.

	// exitsyscall, since it would otherwise be free to move us to
	// a different M. The call to unlockOSThread is in this function
	// after cgocallbackg1, or in the case of panicking, in unwindm.
	lockOSThread()

	checkm := gp.m

	// Save current syscall parameters, so m.winsyscall can be
	// used again if callback decide to make syscall.
	winsyscall := gp.m.winsyscall

			// Warning: Do not call UnlockOSThread! Notably, netns.Do does call this.
			runtime.LockOSThread()
			if err := setupSandbox(); err != nil {
				return err
			}
			// Mark we have actually run the command. This lets us distinguish from a failure in setupSandbox() vs f()
			executed = true
			return f()

// new process, so it normally starts with the program name.
//
// If the calling goroutine has locked the operating system thread
// with [runtime.LockOSThread] and modified any inheritable OS-level
// thread state (for example, Linux or Plan 9 name spaces), the new
// process will inherit the caller's thread state.
//

		err   error
	}
	ch := make(chan result) // unbuffered
	go func() {
		if err := acquireThread(ctx); err != nil {
			ch <- result{err: mapErr(err)}
			return
		}
		defer releaseThread()
		runtime.LockOSThread()
		defer runtime.UnlockOSThread()
		proto, err := getprotobyname(name)
		select {
		case ch <- result{proto: proto, err: err}:
		case <-ctx.Done():
		}
	}()
	select {
	case r := <-ch:

	}
}

func TestCallbackGC(t *testing.T) {
	nestedCall(t, runtime.GC)
}

func TestCallbackPanicLocked(t *testing.T) {
	runtime.LockOSThread()
	defer runtime.UnlockOSThread()

	if !runtime.LockedOSThread() {
		t.Fatal("runtime.LockOSThread didn't")
	}
	defer func() {
		s := recover()
		if s == nil {
			t.Fatal("did not panic")
		}
		if s.(string) != "callback panic" {

func startProcess(argv0 string, argv []string, attr *ProcAttr) (pid int, err error) {
	type forkRet struct {
		pid int
		err error
	}

	forkc := make(chan forkRet, 1)
	go func() {
		runtime.LockOSThread()
		var ret forkRet

		ret.pid, ret.err = forkExec(argv0, argv, attr)
		// If fork fails there is nothing to wait for.
		if ret.err != nil || ret.pid == 0 {
			forkc <- ret
			return
		}

	Size        int // Size.
}

type SysProcAttr struct {
	Chroot     string      // Chroot.
	Credential *Credential // Credential.
	// Ptrace tells the child to call ptrace(PTRACE_TRACEME).
	// Call runtime.LockOSThread before starting a process with this set,
	// and don't call UnlockOSThread until done with PtraceSyscall calls.
	Ptrace bool
	Setsid bool // Create session.
	// Setpgid sets the process group ID of the child to Pgid,

	lockedg       guintptr
	createstack   [32]uintptr // stack that created this thread, it's used for StackRecord.Stack0, so it must align with it.
	lockedExt     uint32      // tracking for external LockOSThread
	lockedInt     uint32      // tracking for internal lockOSThread
	nextwaitm     muintptr    // next m waiting for lock

	mLockProfile mLockProfile // fields relating to runtime.lock contention