Kernelnewbies Digest, Vol 37, Issue 37

[Frank Martinez]

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On Sat, Dec 28, 2013 at 12:00 PM,
<kernelnewbies-request at kernelnewbies.org>wrote:

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>    1. Re: Can't cleanly unload driver (Valdis.Kletnieks at vt.edu)
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>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sat, 28 Dec 2013 00:13:08 -0500
> From: Valdis.Kletnieks at vt.edu
> Subject: Re: Can't cleanly unload driver
> To: Eric Fowler <eric.fowler at gmail.com>
> Cc: kernelnewbies at kernelnewbies.org
> Message-ID: <221197.1388207588 at turing-police.cc.vt.edu>
> Content-Type: text/plain; charset="us-ascii"
>
> On Fri, 27 Dec 2013 19:33:50 -0800, Eric Fowler said:
>
> > I suspect I am doing something wrong in the code with
> > register/unregister_chrdev(), but I have been over that code a million
> > times. It looks fine.
> >
> > Now:
> > insmod the device, OK
> > rmmod the device, OK
> > Check /proc/devices , device # is present
> > insmod the device again, fails with ERROR: could not insert module
> > ./foobar.ko: Device or resource busy
>
> It does smell like an unregister issue.  You may want to try adding
> printk() calls to print out the return code from register and unregister.
> I'm willing to bet that (a) the unegister is failing because somebody
> still has a reference on the device, and (b) the second register call fails
> because the device already exists, causing your module_init() to bail out.
>
> The fun is that you may not have taken a reference on the device directly
> yourself - you may have called some other get_foo() that ends up taking an
> implicit reference under the covers, causing issues when you fail to call
> put_foo() at the right place...
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> End of Kernelnewbies Digest, Vol 37, Issue 37
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