Re: [PATCH v2 13/13] nubus: Add support for the driver model

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Nov 23, 2017 at 11:24:38AM +1100, Finn Thain wrote:
> On Mon, 20 Nov 2017, I wrote:
> 
> > > You need to free up the memory allocated, and I don't see that 
> > > happening here ... The kernel should yell at you ...
> 
> > 
> >                 WARN(1, KERN_ERR "Device '%s' does not have a release() "
> >                         "function, it is broken and must be fixed.\n",
> >                         dev_name(dev));
> > 
> > This won't fire unless device_del() is called, right?
> 
> Sorry, I should have written, "This won't fire unless device_unregister() 
> is called, right?" -- though I guess it could be any call to put_device().
> 
> If need be I can add code to cleanly tear down the bus devices and the 
> associated linked lists and procfs structures, just prior to kernel 
> termination, as a kernel exitcall. But I don't see this pattern in use.

When the kernel shuts down, no, the devices are not removed.

But what happens when the bus code is unloaded if it is built as a
module?  The devices will be removed then.  Or they should be.

So please implement the remove device code path, just because some other
busses are buggy that way does not mean you need to duplicate their
incorrect behavior.


> 
> It's not clear to me that the extra complexity is worth it. This may 
> explain the other devices which never get unregistered (e.g. rtc_device, 
> rtc_efi_dev, etc.)
> 
> I've read Documentation/driver-model/ and watched your presentations on 
> this topic but it's unclear to me whether you are saying in this thread 
> that calling device_unregister() is mandatory.
> 
> It sounds like you are saying that a non-NULL device.release method is 
> mandatory (which is easily solved with an empty function). But 
> Documentation/driver-model/porting.txt says the release method is 
> optional.

If you provide a non-NULL empty release function, you get to be made fun
of, as per the in-kernel kobject documentation.  The kernel is trying to
save you from yourself, that warning is not there just to try to work
around.

thanks,

greg k-h