Actually, I was working with a homegrown makefile. I made the change you recommended and am still having the problem. I am thinking now about something else as being the problem. Is this code legitimate? //// file scope struct cdev my_cdev; ///inside init function cdev_init(&my_cdev, ....); cdev_add(&my_cdev, ....); ///exit fxn cdev_del(&my_cdev); In other words, the memory for the cdev struct comes from static memory for the driver, not a call to cdev_alloc() or kmalloc(). On Mon, Dec 30, 2013 at 10:18 AM, Rajat Sharma <fs.rajat@gmail.com> wrote:
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@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@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...
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