Date: Fri, 25 Jul 2003 12:26:51 -0700
From: Stephen Hemminger <shemminger@osdl.org>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: davem@redhat.com, arjanv@redhat.com, torvalds@transmeta.com,
       greg@kroah.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Remove module reference counting.
Message-Id: <20030725122651.4aedc768.shemminger@osdl.org>
In-Reply-To: <20030725173900.D7DE12C2A9@lists.samba.org>
References: <20030725173900.D7DE12C2A9@lists.samba.org>
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On Fri, 25 Jul 2003 04:00:18 +1000
Rusty Russell <rusty@rustcorp.com.au> wrote:

> Hi all,
> 
> 	When the initial module patch was submitted, it made modules
> start isolated, so they would not be accessible until (if)
> initialization had succeeded.  This broke partition scanning, and was
> immediately reverted, leaving us with a module reference count scheme
> identical to the previous one (just a faster implementation): we still
> have cases where modules can be access on failed load.
> 
> 	Then Dave decided that the work of reference counting network
> driver modules everywhere is too invasive, so network driver modules
> now have zero reference counts always.  The idea is that if you don't
> want the module removed, don't do it.  ie. only remove the module if
> there's a bug, or you want to replace it.
> 
> 	If module removal is to be a rare and unusual event, it
> doesn't seem so sensible to go to great lengths in the code to handle
> just that case.  In fact, it's easier to leave the module memory in
> place, and not have the concept of parts of the kernel text (and some
> types of kernel data) vanishing.
> 
> Polite feedback welcome,
> Rusty.
> --

There are two possible objections to this:
 * Some developers keep the same kernel running and load/unload then reload
   a new driver when debugging. This would break probably or at least cause
   a large amount of kernel growth. Not that big an issue for me personally
   but driver writers seem to get hit with all the changes.

 * Drivers might get sloppy about not cleaning up timers and data structures
   -- more than they are already.  You might want to have a kernel debug option
   that overwrite's the unloaded text with something guaranteed to cause an 
   oops.


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