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From: Keith Owens <kaos@ocs.com.au>
To: Patrick Mochel <mochel@osdl.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Driverfs updates 
In-reply-to: Your message of "Mon, 08 Jul 2002 11:41:52 MST."
             <Pine.LNX.4.33.0207051554580.961-100000@geena.pdx.osdl.net> 
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Date: Tue, 09 Jul 2002 09:33:24 +1000
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On Mon, 8 Jul 2002 11:41:52 -0700 (PDT), 
Patrick Mochel <mochel@osdl.org> wrote:
>- Add struct module * owner field to struct device_driver
>- Change {get,put}_driver to use it

struct device_driver * get_driver(struct device_driver * drv)
{
        if (drv && drv->owner)
                if (!try_inc_mod_count(drv->owner))
                        return NULL;
        return drv;
}

is racy.  The module can be unloaded after if (drv->owner) and before
try_inc_mod_count.  To prevent that race, drv itself must be locked
around calls to get_driver().

The "normal" method is to have a high level lock that controls the drv
list and to take that lock in the register and unregister routines and
around the call to try_inc_mod_count.  drv->bus->lock is no good,
anything that relies on reading drv without a lock or module reference
count is racy.  I suggest you add a global driverfs_lock.

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