Commit e2e4025b authored by Ivaylo Dimitrov's avatar Ivaylo Dimitrov Committed by Greg Kroah-Hartman
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tty: n_gsm: wait until channel 0 is ready 



Currently code does not wait for channel 0 open sequence to complete before
pushing data to the other channels. Also, if userland opens tty, it will
receive EL2NSYNC. Both issues result in hard to predict initialization
sequence and possible userland failures.

Fix that by waiting channel 0 open sequence to complete before attempting
opening of the other channels. Also, if tty open() is attempted while
channel 0 is opening, wait until sequence is complete before returning to
userland.

Signed-off-by: default avatarIvaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>
Signed-off-by: default avatarTony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20241228150100.100354-2-ivo.g.dimitrov.75@gmail.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent d78a8999

drivers/tty/n_gsm.c

+23 −8
Original line number Diff line number Diff line
@@ -2244,13 +2244,16 @@ static void gsm_dlci_t1(struct timer_list *t) 
		break;

	case DLCI_OPENING:

		if (dlci->retries) {

			if (!dlci->addr || !gsm->dlci[0] ||

			    gsm->dlci[0]->state != DLCI_OPENING) {

				dlci->retries--;

				gsm_command(dlci->gsm, dlci->addr, SABM|PF);

			}



			mod_timer(&dlci->t1, jiffies + gsm->t1 * HZ / 100);

		} else if (!dlci->addr && gsm->control == (DM | PF)) {

			if (debug & DBG_ERRORS)

				pr_info("DLCI %d opening in ADM mode.\n",

					dlci->addr);

				pr_info("DLCI 0 opening in ADM mode.\n");

			dlci->mode = DLCI_MODE_ADM;

			gsm_dlci_open(dlci);

		} else {
@@ -2308,6 +2311,8 @@ static void gsm_dlci_begin_open(struct gsm_dlci *dlci) 
		dlci->retries = gsm->n2;

		if (!need_pn) {

			dlci->state = DLCI_OPENING;

			if (!dlci->addr || !gsm->dlci[0] ||

			    gsm->dlci[0]->state != DLCI_OPENING)

				gsm_command(gsm, dlci->addr, SABM|PF);

		} else {

			/* Configure DLCI before setup */
@@ -4251,7 +4256,7 @@ static const struct tty_port_operations gsm_port_ops = { 
static int gsmtty_install(struct tty_driver *driver, struct tty_struct *tty)

{

	struct gsm_mux *gsm;

	struct gsm_dlci *dlci;

	struct gsm_dlci *dlci, *dlci0;

	unsigned int line = tty->index;

	unsigned int mux = mux_line_to_num(line);

	bool alloc = false;
@@ -4274,10 +4279,20 @@ static int gsmtty_install(struct tty_driver *driver, struct tty_struct *tty) 
	perspective as we don't have to worry about this

	if DLCI0 is lost */

	mutex_lock(&gsm->mutex);

	if (gsm->dlci[0] && gsm->dlci[0]->state != DLCI_OPEN) {



	dlci0 = gsm->dlci[0];

	if (dlci0 && dlci0->state != DLCI_OPEN) {

		mutex_unlock(&gsm->mutex);



		if (dlci0->state == DLCI_OPENING)

			wait_event(gsm->event, dlci0->state != DLCI_OPENING);



		if (dlci0->state != DLCI_OPEN)

			return -EL2NSYNC;



		mutex_lock(&gsm->mutex);

	}



	dlci = gsm->dlci[line];

	if (dlci == NULL) {

		alloc = true;