Send data to user space daemon from kext

Hello,

I'm using kernel control API to send data to a user space daemon from kext. It works most of the time, but on some occation, the ctl_enqueuedata() function return the errno code 12(ENOMEM), which is a little weird. This is the snippet in my code.

// in kext
errno_t error = ctl_enqueuedata(gCtlInfo.clientCtlRef, gCtlInfo.unit, (void*)notify, sizeof(struct CONFIG_NOTIFY), CTL_DATA_EOR);
if (0 != error)
{
    KEXT_LOG_ERROR("Failed to talk to user space daemon(error=%d).", error);
    return result;
}

// in user space daemon
dispatch_source_t readSource = dispatch_source_create(DISPATCH_SOURCE_TYPE_READ, g_sock, 0, g_globalQueue);
dispatch_source_set_event_handler_f(readSource, (dispatch_function_t)dataArrived);
dispatch_resume(readSource);

ssize_t n = recv(sock, (void*)notify, sizeof(struct CONFIG_NOTIFY), 0);
if (n < sizeof(struct CONFIG_NOTIFY))
{
    SPDLOG_ERROR("recv() failed, error: {}", strerror(errno));
    return -1;
}

I just send a fixed-size struct from kext several times per minute, not much data I think. And I also set the buffer large enough in the kern_ctl_reg structure.

static struct kern_ctl_reg gCtlReg =
{
    BUNDLE_ID,
    0,
    0,
    0,
    0x800000, //2048KB
    0x800000,
    ctl_connect,
    ctl_disconnect,
    NULL,
    ctl_set,
    NULL 
};

BTW, my app runs on macOS 10.14.6 with 16GB ram.

What could be the possible reason for this failure? Thanks!