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

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Date: Mon, 6 May 2024 21:26:02 +0200
From: Heiko Carstens <hca@...ux.ibm.com>
To: Arnd Bergmann <arnd@...db.de>
Cc: Nathan Chancellor <nathan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>, gor@...ux.ibm.com,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>, wintera@...ux.ibm.com,
        twinkler@...ux.ibm.com, linux-s390@...r.kernel.org,
        Netdev <netdev@...r.kernel.org>, llvm@...ts.linux.dev,
        patches@...ts.linux.dev
Subject: Re: [PATCH 1/3] s390/vmlogrdr: Remove function pointer cast

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.