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Date: Sun, 5 Nov 2000 01:38:09 +0100
From: Andi Kleen <ak@suse.de>
To: Jeff Garzik <jgarzik@mandrakesoft.com>
Cc: Andi Kleen <ak@suse.de>, "Hen, Shmulik" <shmulik.hen@intel.com>,
        "'LKML'" <linux-kernel@vger.kernel.org>,
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Subject: Re: Locking Between User Context and Soft IRQs in 2.4.0
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In-Reply-To: <3A044256.D8CD063C@mandrakesoft.com>; from jgarzik@mandrakesoft.com on Sat, Nov 04, 2000 at 12:07:34PM -0500
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On Sat, Nov 04, 2000 at 12:07:34PM -0500, Jeff Garzik wrote:
> Andi Kleen wrote:
> > All the MOD_INC/DEC_USE_COUNT are done inside the modules themselves. There
> > is nothing that would a driver prevent from being unloaded on a different
> > CPU while it is already executing in ->open but has not yet executed the add
> > yet or after it has executed the _DEC but it is still running in module code
> > Normally the windows are pretty small, but very long running interrupt
> > on one CPU hitting exactly in the wrong moment can change that.
> 
> Module unload calls unregister_netdev, which grabs rtnl_lock.
> dev->open runs under rtnl_lock.
> 
> Given this, how can the driver be unloaded if dev->open is running?

It does not help, because when the semaphore synchronizes it is already
too late -- free_module already did the zero module count check and 
nothing is going to stop it from unloading.

-Andi

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