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Date: Tue, 2 Jul 2002 18:23:12 -0400 (EDT)
From: Alexander Viro <viro@math.psu.edu>
To: Keith Owens <kaos@ocs.com.au>
cc: linux-kernel@vger.kernel.org
Subject: Re: RE2: [OKS] Module removal 
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On Tue, 2 Jul 2002, Keith Owens wrote:

> Incrementing the use count at registration time is no good, it stops
> the module being unloaded.  Operations are deregistered at rmmod time.
> Setting the use count at registration prevents rmmod from removing the
> module, so you cannot deregister the operations.  Catch 22.

Right.  So you should use try_inc_mod_count() before dereferencing the
registered pointers and treat failure as "not found".
 
> Module unload is not racy on UP without preempt.  It is racy on SMP or
> with preempt.  It used to be safe on SMP because almost everything was
> under the BKL, but that protection no longer exists.

<wry> You forgot "as long as nothing blocks". Which is more than brittle -
code changes routinely violate such warranties. </wry>

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