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author | Peter Hurley <peter@hurleysoftware.com> | 2013-03-11 16:44:40 -0400 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2013-03-18 16:48:42 -0700 |
commit | ebc9baed42e42f9b51cf61672b7afb72f068d523 (patch) | |
tree | 2438eccbfddbfde6ff8a388f2dcf049913b4db8e /drivers/tty | |
parent | 8842dda2366d3d0c97646102768831f9b0ffd712 (diff) | |
download | op-kernel-dev-ebc9baed42e42f9b51cf61672b7afb72f068d523.zip op-kernel-dev-ebc9baed42e42f9b51cf61672b7afb72f068d523.tar.gz |
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: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty')
-rw-r--r-- | drivers/tty/tty_ldisc.c | 69 |
1 files changed, 35 insertions, 34 deletions
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index 328ff5b..9362a10 100644 --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -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); } |