[BUG] n_gsm: possible recursive locking detected
From: Martin HundebÃll
Date: Wed Jul 17 2019 - 05:40:27 EST
Hi,
The GSM0710 line discipline driver triggers a lockdep warning when
disabling the ldisc while holding a multiplexed virtual tty open:
============================================
WARNING: possible recursive locking detected
5.2.0-00114-gdab52e30156b #6 Not tainted
--------------------------------------------
cmux/263 is trying to acquire lock:
e1e23b18 (&tty->legacy_mutex){+.+.}, at: __tty_hangup.part.0+0x58/0x27c
but task is already holding lock:
d6eddf48 (&tty->legacy_mutex){+.+.}, at: tty_set_ldisc+0x3c/0x1bc
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&tty->legacy_mutex);
lock(&tty->legacy_mutex);
*** DEADLOCK ***
May be due to missing lock nesting notation
3 locks held by cmux/263:
#0: d6eddf48 (&tty->legacy_mutex){+.+.}, at: tty_set_ldisc+0x3c/0x1bc
#1: f28bead9 (&tty->ldisc_sem){++++}, at: tty_ldisc_lock+0x50/0x74
#2: e5d20e4f (&gsm->mutex){+.+.}, at: gsm_cleanup_mux+0x9c/0x15c
stack backtrace:
CPU: 0 PID: 263 Comm: cmux Not tainted 5.2.0-00114-gdab52e30156b #6
Hardware name: Freescale i.MX6 Ultralite (Device Tree)
[<c011184c>] (unwind_backtrace) from [<c010cc74>] (show_stack+0x10/0x14)
[<c010cc74>] (show_stack) from [<c0852488>] (dump_stack+0xd4/0x108)
[<c0852488>] (dump_stack) from [<c017be90>] (__lock_acquire+0x6ec/0x1e84)
[<c017be90>] (__lock_acquire) from [<c017ddc4>] (lock_acquire+0xcc/0x204)
[<c017ddc4>] (lock_acquire) from [<c086e9d0>] (__mutex_lock+0x64/0x90c)
[<c086e9d0>] (__mutex_lock) from [<c086f294>] (mutex_lock_nested+0x1c/0x24)
[<c086f294>] (mutex_lock_nested) from [<c04c02fc>]
(__tty_hangup.part.0+0x58/0x27c)
[<c04c02fc>] (__tty_hangup.part.0) from [<c04ce718>]
(gsm_cleanup_mux+0xe8/0x15c)
[<c04ce718>] (gsm_cleanup_mux) from [<c04ce7d4>] (gsmld_close+0x48/0x90)
[<c04ce7d4>] (gsmld_close) from [<c04c7e24>] (tty_set_ldisc+0xb8/0x1bc)
[<c04c7e24>] (tty_set_ldisc) from [<c04c0b70>] (tty_ioctl+0x640/0xcb0)
[<c04c0b70>] (tty_ioctl) from [<c0297e68>] (do_vfs_ioctl+0x41c/0xa5c)
[<c0297e68>] (do_vfs_ioctl) from [<c02984dc>] (ksys_ioctl+0x34/0x60)
[<c02984dc>] (ksys_ioctl) from [<c0101000>] (ret_fast_syscall+0x0/0x28)
Exception stack(0xc8ce1fa8 to 0xc8ce1ff0)
1fa0: 00438000 00000000 00000003 00005423 beb6cc04
beb6cc04
1fc0: 00438000 00000000 00000000 00000036 00000000 00000000 00438000
beb6ccd4
1fe0: 00438048 beb6cbfc 00427684 b6f58b88
Steps to reproduce using the attached cmux util:
root@iwg26:~# ./cmux &
[1] 254
SERIAL_PORT = /dev/ttymxc0
AT+IFC=2: Ie5 +CFUN: 1 +CPIN: READY Call Ready AT+IFC=2,2 OK
AT+GMM : AT+GMM Quectel_M95 OK
AT : AT OK
AT+IPR=1: AT+IPR=115200&w OK
AT+CMUX=: AT+CMUX=0,0,5,512,10,3,30,10,2 OK
Line dicipline set
root@iwg26:~# cat /dev/gsmtty1 &
[2] 262
root@iwg26:~# kill %1
[ 74.517449] ============================================
[ 74.522769] WARNING: possible recursive locking detected
[ 74.528094] 5.2.0-00114-gdab52e30156b #6 Not tainted
[ 74.533065] --------------------------------------------
<...>
This has supposedly been fixed before in 4d9b109060f6 ("tty: Prevent
deadlock in n_gsm driver"), but the fix was undone in be7065725590
("TTY/n_gsm: Removing the wrong tty_unlock/lock() in gsm_dlci_release()")
--
Kind regards,
Martin HundebÃll
Embedded Linux Consultant
+45 61 65 54 61
martin@xxxxxxxxxx
Geanix ApS
https://geanix.com
DK39600706
/**
* Cmux
* Enables GSM 0710 multiplex using n_gsm
*
* Copyright (C) 2013 - Rtone - Nicolas Le Manchet <nicolaslm@xxxxxxxx>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
#include <stdlib.h>
#include <stdio.h>
#include <stdarg.h>
#include <string.h>
#include <unistd.h>
#include <termios.h>
#include <net/if.h>
#include <linux/types.h>
#include <linux/gsmmux.h>
#include <sys/sysmacros.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <err.h>
#include <signal.h>
/* n_gsm ioctl */
#ifndef N_GSM0710
# define N_GSM0710 21
#endif
/* attach a line discipline ioctl */
#ifndef TIOCSETD
# define TIOCSETD 0x5423
#endif
/* serial port of the modem */
#define SERIAL_PORT "/dev/ttymxc0"
/* line speed */
#define LINE_SPEED B115200
/* maximum transfert unit (MTU), value in bytes */
#define MTU 512
/**
* whether or not to create virtual TTYs for the multiplex
* 0 : do not create
* 1 : create
*/
#define CREATE_NODES 0
/* number of virtual TTYs to create (most modems can handle up to 4) */
#define NUM_NODES 4
/* name of the virtual TTYs to create */
#define BASENAME_NODES "/dev/ttyGSM"
/* name of the driver, used to get the major number */
#define DRIVER_NAME "gsmtty"
/**
* whether or not to print debug messages to stderr
* 0 : debug off
* 1 : debug on
*/
#define DEBUG 1
/**
* whether or not to detach the program from the terminal
* 0 : do not daemonize
* 1 : daemonize
*/
#define DAEMONIZE 0
/* size of the reception buffer which gets data from the serial line */
#define SIZE_BUF 256
/**
* Prints debug messages to stderr if debug is wanted
*/
static void dbg(char *fmt, ...) {
va_list args;
if (DEBUG) {
fflush(NULL);
va_start(args, fmt);
vfprintf(stderr, fmt, args);
va_end(args);
fprintf(stderr, "\n");
fflush(NULL);
}
return;
}
/**
* Sends an AT command to the specified line and gets its result
* Returns 0 on success
* -1 on failure
*/
int send_at_command(int serial_fd, char *command) {
char buf[SIZE_BUF];
int r;
/* write the AT command to the serial line */
if (write(serial_fd, command, strlen(command)) <= 0)
err(EXIT_FAILURE, "Cannot write to %s", SERIAL_PORT);
/* wait a bit to allow the modem to rest */
sleep(1);
/* read the result of the command from the modem */
memset(buf, 0, sizeof(buf));
r = read(serial_fd, buf, sizeof(buf));
if (r == -1)
err(EXIT_FAILURE, "Cannot read %s", SERIAL_PORT);
/* if there is no result from the modem, return failure */
if (r == 0) {
dbg("%s\t: No response", command);
return -1;
}
/* if we have a result and want debug info, strip CR & LF out from the output */
if (DEBUG) {
int i;
char bufp[SIZE_BUF];
memcpy(bufp, buf, sizeof(buf));
for(i=0; i<strlen(bufp); i++) {
if (bufp[i] == '\r' || bufp[i] == '\n')
bufp[i] = ' ';
}
dbg("%s\t: %s", command, bufp);
}
/* if the output shows "OK" return success */
if (strstr(buf, "OK\r") != NULL) {
return 0;
}
return -1;
}
/**
* Function raised by signal catching
*/
void signal_callback_handler(int signum) {
return;
}
/**
* Gets the major number of the driver device
* Returns the major number on success
* -1 on failure
*/
int get_major(char *driver) {
FILE *fp;
char *line = NULL;
size_t len = 0;
ssize_t read;
char device[20];
int major = -1;
/* open /proc/devices file */
if ((fp = fopen("/proc/devices", "r")) == NULL)
err(EXIT_FAILURE, "Cannot open /proc/devices");
/* read the file line by line */
while ((major == -1) && (read = getline(&line, &len, fp)) != -1) {
/* if the driver name string is found in the line, try to get the major */
if (strstr(line, driver) != NULL) {
if (sscanf(line,"%d %s\n", &major, device) != 2)
major = -1;
}
/* free the line before getting a new one */
if (line) {
free(line);
line = NULL;
}
}
/* close /proc/devices file */
fclose(fp);
return major;
}
/**
* Creates nodes for the virtual TTYs
* Returns the number of nodes created
*/
int make_nodes(int major, char *basename, int number_nodes) {
int minor, created = 0;
dev_t device;
char node_name[15];
mode_t oldmask;
/* set a new mask to get 666 mode and stores the old one */
oldmask = umask(0);
for (minor=1; minor<number_nodes+1; minor++) {
/* append the minor number to the base name */
sprintf(node_name, "%s%d", basename, minor);
/* store a device info with major and minor */
device = makedev(major, minor);
/* create the actual character node */
if (mknod(node_name, S_IFCHR | 0666, device) != 0) {
warn("Cannot create %s", node_name);
} else {
created++;
dbg("Created %s", node_name);
}
}
/* revert the mask to the old one */
umask(oldmask);
return created;
}
/**
* Removes previously created TTY nodes
* Returns nothing, it doesn't really matter if it fails
*/
void remove_nodes(char *basename, int number_nodes) {
int node;
char node_name[15];
for (node=1; node<number_nodes+1; node++) {
/* append the minor number to the base name */
sprintf(node_name, "%s%d", basename, node);
/* unlink the actual character node */
dbg("Removing %s", node_name);
if (unlink(node_name) == -1)
warn("Cannot remove %s", node_name);
}
return;
}
int main(void) {
int serial_fd, major;
struct termios tio;
int ldisc = N_GSM0710;
int ldisc_save;
struct gsm_config gsm;
char atcommand[40];
//char disconnect[] = {0xf9, 0x03, 0xef, 0x03, 0xc3, 0x16, 0xf9};
char disconnect[] = {0xf9, 0x03, 0xef, 0x05, 0xc3, 0x01, 0xf2, 0xf9};
/* print global parameters */
dbg("SERIAL_PORT = %s", SERIAL_PORT);
/* open the serial port */
serial_fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_NDELAY);
if (serial_fd == -1)
err(EXIT_FAILURE, "Cannot open %s", SERIAL_PORT);
/* get the current attributes of the serial port */
if (tcgetattr(serial_fd, &tio) == -1)
err(EXIT_FAILURE, "Cannot get line attributes");
/* set the new attrbiutes */
tio.c_iflag = 0;
tio.c_oflag = 0;
tio.c_cflag = CS8 | CREAD | CLOCAL;
tio.c_cflag |= CRTSCTS;
tio.c_lflag = 0;
tio.c_cc[VMIN] = 1;
tio.c_cc[VTIME] = 0;
/* write the speed of the serial line */
if (cfsetospeed(&tio, LINE_SPEED) < 0 || cfsetispeed(&tio, LINE_SPEED) < 0)
err(EXIT_FAILURE, "Cannot set line speed");
/* write the attributes */
if (tcsetattr(serial_fd, TCSANOW, &tio) == -1)
err(EXIT_FAILURE, "Cannot set line attributes");
/**
* Send AT commands to put the modem in CMUX mode.
* This is vendor specific and should be changed
* to fit your modem needs.
* The following matches Quectel M95.
*/
if (send_at_command(serial_fd, "AT+IFC=2,2\r") == -1)
errx(EXIT_FAILURE, "AT+IFC=2,2: bad response");
if (send_at_command(serial_fd, "AT+GMM\r") == -1)
warnx("AT+GMM: bad response");
if (send_at_command(serial_fd, "AT\r") == -1)
warnx("AT: bad response");
if (send_at_command(serial_fd, "AT+IPR=115200&w\r") == -1)
errx(EXIT_FAILURE, "AT+IPR=115200&w: bad response");
sprintf(atcommand, "AT+CMUX=0,0,5,%d,10,3,30,10,2\r", MTU);
if (send_at_command(serial_fd, atcommand) == -1)
errx(EXIT_FAILURE, "Cannot enable modem CMUX");
if (ioctl(serial_fd, TIOCGETD, &ldisc_save) < 0)
err(EXIT_FAILURE, "Cannot get current line discipline");
/* use n_gsm line discipline */
sleep(2);
if (ioctl(serial_fd, TIOCSETD, &ldisc) < 0)
err(EXIT_FAILURE, "Cannot set line dicipline. Is 'n_gsm' module registred?");
/* get n_gsm configuration */
if (ioctl(serial_fd, GSMIOC_GETCONF, &gsm) < 0)
err(EXIT_FAILURE, "Cannot get GSM multiplex parameters");
/* set and write new attributes */
gsm.initiator = 1;
gsm.encapsulation = 0;
gsm.mru = MTU;
gsm.mtu = MTU;
gsm.t1 = 10;
gsm.n2 = 3;
gsm.t2 = 30;
gsm.t3 = 10;
if (ioctl(serial_fd, GSMIOC_SETCONF, &gsm) < 0)
err(EXIT_FAILURE, "Cannot set GSM multiplex parameters");
dbg("Line dicipline set");
/* create the virtual TTYs */
if (CREATE_NODES) {
int created;
if ((major = get_major(DRIVER_NAME)) < 0)
errx(EXIT_FAILURE, "Cannot get major number");
if ((created = make_nodes(major, BASENAME_NODES, NUM_NODES)) < NUM_NODES)
warnx("Cannot create all nodes, only %d/%d have been created.", created, NUM_NODES);
}
/* detach from the terminal if needed */
if (DAEMONIZE) {
dbg("Going to background");
if (daemon(0,0) != 0)
err(EXIT_FAILURE, "Cannot daemonize");
}
/* wait to keep the line discipline enabled, wake it up with a signal */
signal(SIGINT, signal_callback_handler);
signal(SIGTERM, signal_callback_handler);
pause();
/* remove the created virtual TTYs */
if (CREATE_NODES) {
remove_nodes(BASENAME_NODES, NUM_NODES);
}
if (ioctl(serial_fd, TIOCSETD, &ldisc_save) < 0)
err(EXIT_FAILURE, "Cannot set initial line dicipline");
if (write(serial_fd, disconnect, sizeof(disconnect)) != sizeof(disconnect))
err(EXIT_FAILURE, "Cannot disable modem CMUX");
/* close the serial line */
close(serial_fd);
return EXIT_SUCCESS;
}