drivers/tty/tty_mutex.c

#include <linux/tty.h>
#include <linux/module.h>
#include <linux/kallsyms.h>
#include <linux/semaphore.h>
#include <linux/sched.h>

/* Legacy tty mutex glue */

/*
 * Getting the big tty mutex.
 */

void __lockfunc tty_lock(struct tty_struct *tty)
{
	if (WARN(tty->magic != TTY_MAGIC, "L Bad %p\n", tty))
		return;
	tty_kref_get(tty);
	mutex_lock(&tty->legacy_mutex);
}
EXPORT_SYMBOL(tty_lock);

void __lockfunc tty_unlock(struct tty_struct *tty)
{
	if (WARN(tty->magic != TTY_MAGIC, "U Bad %p\n", tty))
		return;
	mutex_unlock(&tty->legacy_mutex);
	tty_kref_put(tty);
}
EXPORT_SYMBOL(tty_unlock);

void __lockfunc tty_lock_slave(struct tty_struct *tty)
{
	if (tty && tty != tty->link)
		tty_lock(tty);
}

void __lockfunc tty_unlock_slave(struct tty_struct *tty)
{
	if (tty && tty != tty->link)
		tty_unlock(tty);
}

void tty_set_lock_subclass(struct tty_struct *tty)
{
	lockdep_set_subclass(&tty->legacy_mutex, TTY_LOCK_SLAVE);
}