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From
SubjectRe: Locking Between User Context and Soft IRQs in 2.4.0
Date
On Sun, 05 Nov 2000 12:28:55 +1100, 
Andrew Morton <andrewm@uow.edu.au> wrote:
> CPU0 CPU1
>
> rtnl_lock()
> dev_ifsioc()
> dev_change_flags()
> dev_open();
> dev->open();
> vortex_open()
> sys_delete_module()
> if (!__MOD_IN_USE)
> free_module()

If dev->open() calls try_inc_use_count() before it enters the module
you will lock out concurrent module unload via module unload_lock.
There is no need for another module semaphore.

Also there is no need to test dev->owner, try_inc_use_count() already
does that.

/*
* Call device private open method
*/

ret = -ENODEV;
if (try_inc_mod_count(dev->owner)) {
if (dev->open && (ret = dev->open(dev)) && dev->owner)
__MOD_DEC_USE_COUNT(dev->owner);
}

In dev_close()

/*
* Call device private close method
*/

if (dev->owner)
__MOD_DEC_USE_COUNT(dev->owner);

-
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