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August 13, 2015

Line discipline register and unregister in new kernels

I have a linux kernel driver for serial device, which uses line discipline and char device. Driver works with all old kernels, starting from 3.8 this driver still works, but when I unload it and load again to the memory (modprobe -r bpsctl_mod, after modprobe bpsctl_mod), it crashes the kernel. It can't unregister line discipline, because this line discipline is busy. I use system device, i.e., ttyS0. Here is problematic code:

static struct file* bps_file_open(const char* path, int flags, int rights) {
struct file* filp = NULL;
mm_segment_t oldfs;
oldfs = get_fs();
filp = filp_open(path, flags, rights);
if (IS_ERR(filp))
return NULL;
return filp;
int register_ldisc(void) {
int status;
// Fill in our line protocol discipline, and register it
extbp_drv.ebtty_ldisc.magic = TTY_LDISC_MAGIC;
extbp_drv.ebtty_ldisc.name = BP_LDISC_NAME;
extbp_drv.ebtty_ldisc.flags = 0;
extbp_drv.ebtty_ldisc.open = ebtty_open;
extbp_drv.ebtty_ldisc.close = ebtty_close;
extbp_drv.ebtty_ldisc.read = NULL;
extbp_drv.ebtty_ldisc.write = NULL;
extbp_drv.ebtty_ldisc.ioctl = (int (*)(struct tty_struct *, struct file *,
unsigned int, unsigned long)) ebtty_ioctl;
extbp_drv.ebtty_ldisc.poll = NULL;
extbp_drv.ebtty_ldisc.receive_buf = ebtty_receive_buf;
extbp_drv.ebtty_ldisc.write_wakeup = NULL; //ebtty_write_wakeup;
if ((status = tty_register_ldisc(extbp_drv.line_disc, &extbp_drv.ebtty_ldisc)) == 0) {
extbp_drv.drv_state |= ST_LDISC_REGISTRATED; }
return status;
int ebtty_init (void) {
int status = -1;
if (register_ldisc()) {
err_print(KERN_ERR, DBG_ERROR,
("Can't register line discipline (%d).\n", line_disc));
goto ebtty_init_exit;
status = 0;
if (status) {
dbg_print(KERN_DEBUG, DBG_ERROR, ("Module initialization failed.\n"));
return status;
static void cleanup(void) {
int status;
if ((status = tty_unregister_ldisc(extbp_drv.line_disc)) != 0) {
err_print(KERN_ERR, DBG_ERROR,
("Can't unregister line discipline (err = %d)\n", status));
int init_ebtty_module(void) {
memset(&port_name_path, 0, sizeof(port_name_path));
sprintf((char *)&port_name_path, "//dev//%s", port_name);
fd=bps_file_open((char *)&port_name_path, 0, O_RDWR);
memset((void*)&extbp_drv, 0, sizeof(struct ext_bypass_drv));
extbp_drv.drv_name = BP_MOD_NAME;
extbp_drv.dev_name = port_name;
extbp_drv.line_disc = line_disc;
extbp_drv.wait_data = LAST_CHAR;
extbp_drv.drv_state = 0;
if (!ebtty_init()) {
extbp_drv.ebtty_major = register_chrdev(0, extbp_drv.drv_name, &ebtty_fops);
if (extbp_drv.ebtty_major < 0) {
err_print(KERN_ERR, DBG_ERROR,
("can't get major %d\n", extbp_drv.ebtty_major));
return extbp_drv.ebtty_major;
if (fd != NULL) {
if (!(bps_vfs_ioctl(fd, TIOCSETD, (unsigned long)&line_disc))) {
bps_start_flag = 1;
return 0;
} else {
if (fd)
filp_close(fd, NULL);
return -1;
void exit_ebtty_module(void) {
if (fd) {
filp_close(fd, NULL);
fd = 0;

Please advice, maybe I should use something else, instead of line discipline and char device, or maybe I should register and unregister them other way?

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