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tty: Separate release semantics of ldisc reference

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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: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2013-03-11 16:44:40 -04:00 committed by Greg Kroah-Hartman
parent 8842dda236
commit ebc9baed42
1 changed files with 35 additions and 34 deletions
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69
drivers/tty/tty_ldisc.c
View file

@ -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);
}