On Thu, Aug 07, 2014 at 12:28:58PM +0400, Pavel Emelyanov wrote:
> On 08/07/2014 12:25 PM, Cyrill Gorcunov wrote:
> > Hi guys, could you please explain me the sequence
> >
> > static void release_one_tty(struct work_struct *work)
> > {
> > struct tty_struct *tty =
> > container_of(work, struct tty_struct, hangup_work);
> > struct tty_driver *driver = tty->driver;
> >
> > if (tty->ops->cleanup)
> > tty->ops->cleanup(tty);
> >
> > tty->magic = 0;
> > --> tty_driver_kref_put(driver);
> > --> module_put(driver->owner);
> >
> > why tty_driver_kref_put is called before module_put? As far as I understand
> > tty_driver_kref_put may call the destruct_tty_driver which eventually does
> >
> > static void destruct_tty_driver(struct kref *kref)
> > {
> > struct tty_driver *driver = container_of(kref, struct tty_driver, kref);
> > ...
> > kfree(driver->cdevs);
> > kfree(driver->ports);
> > kfree(driver->termios);
> > kfree(driver->ttys);
> > --> kfree(driver);
> > }
> >
> > so that the module_put(driver->owner) would access freed memory. Should not
> > we
> > call the reverse module_put and then tty_driver_kref_put, or I miss
> > something
> > obvious?
>
> If you put the module it can be unloaded at any time killing the code that
> would
> be potentially required by kref_put.
So how this code supposed to work then? I mean tty_driver_kref_put must never
call
for destruct_tty_driver, otherwise we're accessing freed memory.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
