Commit d2c43890 authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman
Browse files

tty: Add lock/unlock ldisc pair functions 



Just as the tty pair must be locked in a stable sequence
(ie, independent of which is consider the 'other' tty), so must
the ldisc pair be locked in a stable sequence as well.

Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 137084bb

drivers/tty/tty_ldisc.c

+87 −0
Original line number Diff line number Diff line
@@ -31,6 +31,13 @@ 
#define tty_ldisc_debug(tty, f, args...)

#endif



/* lockdep nested classes for tty->ldisc_sem */

enum {

	LDISC_SEM_NORMAL,

	LDISC_SEM_OTHER,

};





/*

 *	This guards the refcounted line discipline lists. The lock

 *	must be taken with irqs off because there are hangup path
@@ -351,6 +358,86 @@ void tty_ldisc_deref(struct tty_ldisc *ld) 
}

EXPORT_SYMBOL_GPL(tty_ldisc_deref);





static inline int __lockfunc

tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)

{

	return ldsem_down_write(&tty->ldisc_sem, timeout);

}



static inline int __lockfunc

tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout)

{

	return ldsem_down_write_nested(&tty->ldisc_sem,

				       LDISC_SEM_OTHER, timeout);

}



static inline void tty_ldisc_unlock(struct tty_struct *tty)

{

	return ldsem_up_write(&tty->ldisc_sem);

}



static int __lockfunc

tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,

			    unsigned long timeout)

{

	int ret;



	if (tty < tty2) {

		ret = tty_ldisc_lock(tty, timeout);

		if (ret) {

			ret = tty_ldisc_lock_nested(tty2, timeout);

			if (!ret)

				tty_ldisc_unlock(tty);

		}

	} else {

		/* if this is possible, it has lots of implications */

		WARN_ON_ONCE(tty == tty2);

		if (tty2 && tty != tty2) {

			ret = tty_ldisc_lock(tty2, timeout);

			if (ret) {

				ret = tty_ldisc_lock_nested(tty, timeout);

				if (!ret)

					tty_ldisc_unlock(tty2);

			}

		} else

			ret = tty_ldisc_lock(tty, timeout);

	}



	if (!ret)

		return -EBUSY;



	set_bit(TTY_LDISC_HALTED, &tty->flags);

	if (tty2)

		set_bit(TTY_LDISC_HALTED, &tty2->flags);

	return 0;

}



static void __lockfunc

tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2)

{

	tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT);

}



static void __lockfunc tty_ldisc_unlock_pair(struct tty_struct *tty,

					     struct tty_struct *tty2)

{

	tty_ldisc_unlock(tty);

	if (tty2)

		tty_ldisc_unlock(tty2);

}



static void __lockfunc tty_ldisc_enable_pair(struct tty_struct *tty,

					     struct tty_struct *tty2)

{

	clear_bit(TTY_LDISC_HALTED, &tty->flags);

	if (tty2)

		clear_bit(TTY_LDISC_HALTED, &tty2->flags);



	tty_ldisc_unlock_pair(tty, tty2);

}





/**

 *	tty_ldisc_enable	-	allow ldisc use

 *	@tty: terminal to activate ldisc on