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Commit ebc9baed authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman
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tty: Separate release semantics of ldisc reference 



tty_ldisc_ref()/tty_ldisc_unref() have usage semantics
equivalent to down_read_trylock()/up_read(). Only
callers of tty_ldisc_put() are performing the additional
operations necessary for proper ldisc teardown, and then only
after ensuring no outstanding 'read lock' remains.

Thus, tty_ldisc_unref() should never be the last reference;
WARN if it is. Conversely, tty_ldisc_put() should never be
destructing if the use count != 1.

Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 8842dda2

drivers/tty/tty_ldisc.c

+35 −34
Original line number Diff line number Diff line
@@ -49,37 +49,6 @@ static inline struct tty_ldisc *get_ldisc(struct tty_ldisc *ld) 
	return ld;

}



static void put_ldisc(struct tty_ldisc *ld)

{

	unsigned long flags;



	if (WARN_ON_ONCE(!ld))

		return;



	/*

	 * If this is the last user, free the ldisc, and

	 * release the ldisc ops.

	 *

	 * We really want an "atomic_dec_and_raw_lock_irqsave()",

	 * but we don't have it, so this does it by hand.

	 */

	raw_spin_lock_irqsave(&tty_ldisc_lock, flags);

	if (atomic_dec_and_test(&ld->users)) {

		struct tty_ldisc_ops *ldo = ld->ops;



		ldo->refcount--;

		module_put(ldo->owner);

		raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);



		kfree(ld);

		return;

	}

	raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);



	if (waitqueue_active(&ld->wq_idle))

		wake_up(&ld->wq_idle);

}



/**

 *	tty_register_ldisc	-	install a line discipline

 *	@disc: ldisc number
@@ -363,13 +332,45 @@ EXPORT_SYMBOL_GPL(tty_ldisc_ref); 


void tty_ldisc_deref(struct tty_ldisc *ld)

{

	put_ldisc(ld);

	unsigned long flags;



	if (WARN_ON_ONCE(!ld))

		return;



	raw_spin_lock_irqsave(&tty_ldisc_lock, flags);

	/*

	 * WARNs if one-too-many reader references were released

	 * - the last reference must be released with tty_ldisc_put

	 */

	WARN_ON(atomic_dec_and_test(&ld->users));

	raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);



	if (waitqueue_active(&ld->wq_idle))

		wake_up(&ld->wq_idle);

}

EXPORT_SYMBOL_GPL(tty_ldisc_deref);



/**

 *	tty_ldisc_put		-	release the ldisc

 *

 *	Complement of tty_ldisc_get().

 */

static inline void tty_ldisc_put(struct tty_ldisc *ld)

{

	put_ldisc(ld);

	unsigned long flags;



	if (WARN_ON_ONCE(!ld))

		return;



	raw_spin_lock_irqsave(&tty_ldisc_lock, flags);



	/* unreleased reader reference(s) will cause this WARN */

	WARN_ON(!atomic_dec_and_test(&ld->users));



	ld->ops->refcount--;

	module_put(ld->ops->owner);

	kfree(ld);

	raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);

}



/**
@@ -1001,7 +1002,7 @@ void tty_ldisc_init(struct tty_struct *tty) 
 */

void tty_ldisc_deinit(struct tty_struct *tty)

{

	put_ldisc(tty->ldisc);

	tty_ldisc_put(tty->ldisc);

	tty_ldisc_assign(tty, NULL);

}