Can't cleanly unload driver

[Rajat Sharma]

Hi Eric,

I have seen some errors with module reference counting with a nicely
written code, but culprit for my case was a missing compilation flag
-DMODULE which gives definition of THIS_MODULE, otherwise it is null e.g.
for modules which are compiled in kernel, so they are never unloaded.
Unless you have some customization done to Makefiles, this definition
should be included, but its anyways good to double check and rule out this
possibility.

-Rajat


On Mon, Dec 30, 2013 at 9:48 AM, Eric Fowler <eric.fowler at gmail.com> wrote:

> Still working on this. Here is some dmesg spew:
>
> [  514.245846] foobar: module verification failed: signature and/or
> required key missing - tainting kernel
> [  514.245937] kobject: 'foobar' (f7f060c8): kobject_add_internal: parent:
> 'module', set: 'module'
> [  514.245951] kobject: 'holders' (f5ff3d40): kobject_add_internal:
> parent: 'foobar', set: '<NULL>'
> [  514.245981] kobject: 'notes' (f2d25f80): kobject_add_internal: parent:
> 'foobar', set: '<NULL>'
> [  514.245987] kobject: 'foobar' (f7f060c8): kobject_uevent_env
> [  514.245998] kobject: 'foobar' (f7f060c8): fill_kobj_path: path =
> '/module/foobar'
>
> So it looks like kernel validation is failing. I have printk's in my init
> fxn that are never turning up in /var/log/messages, until, weirdly, AFTER I
> remove the device:
>
> <insmod device>
> Dec 30 09:43:03 localhost kernel: [  514.245846] foobar: module
> verification failed: signature and/or required key missing - tainting kernel
> Dec 30 09:43:16 localhost fprintd[1085]: ** Message: No devices in use,
> exit
>
> <rmmod device>
> Dec 30 09:45:53 localhost kernel: [  514.249323] foobar: got device number
> 248, minor is 0   <<<<----THIS IS IN init() fxn
> Dec 30 09:45:53 localhost kernel: [  684.102912] unregister_chrdev(248)
> called for foobar<7>[  684.102927] kobject: '(null)' (f7f06220):
> kobject_cleanup, parent   (null)
>
> <insmod>
> insmod: ERROR: could not insert module ./foobar.ko: Device or resource busy
>
>
>
>
>
>
>
>
> On Fri, Dec 27, 2013 at 9:13 PM, <Valdis.Kletnieks at vt.edu> wrote:
>
>> 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...
>>
>
>
>
> --
> cc:NSA
>
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