Re: [PATCH 1/3] s390/vmlogrdr: Remove function pointer cast

Heiko Carstens
2024-05-06T19:26:17Z

On Thu, Apr 18, 2024 at 09:46:18PM +0200, Arnd Bergmann wrote:
> On Thu, Apr 18, 2024, at 17:15, Heiko Carstens wrote:
> > That doesn't answer my question what prevents the release function
> > from being called after the module has been unloaded.
> >
> > At least back then when the code was added it was a real bug.
>
> I think the way this should work is to have the allocation and
> the release function in the iucv bus driver, with a function
> roughly like
>
> struct device *iucv_alloc_device(char *name,
> const struct attribute_group *attrs,
> void *priv)
> {
> dev = kzalloc(sizeof(struct device), GFP_KERNEL);
> if (!dev)
> return NULL;
>
> dev_set_name(dev, "%s", name);
> dev->bus = &iucv_bus;
> dev->parent = iucv_root;
> dev->groups = attrs;
> dev_set_drvdata(dev, priv);
> dev->release = iucv_free_dev;
>
> return dev;
> }
>
> Now the release function cannot go away as long as any module
> is loaded that links against it, and those modules cannot
> go away as long as the devices are in use.
>
> I don't remember how iucv works, but if there is a way to
> detect which system services exist, then the actual device
> creation should also be separate from the driver using those
> services, with another driver responsible for enumerating
> the existing services and creating those devices.

So, I finally had a deeper look at this, and it looks like the comment
that says that the release function can be called after the module is
unloaded is not correct (anymore?).

I couldn't find any put_device() calls where not also the module reference
count is increased. So I guess Nathan's patches are just fine.

However given your above suggestion, I implemented an iucv_alloc_device()
function to get rid of quite some code duplication, and the casts as well.

I'll send the series for review.