Re: [PATCH v2 1/2] module: update dependencies at try_module_get()

[Greg KH <gregkh@linuxfoundation.org>]

On Sat, Apr 30, 2022 at 11:30:58AM +0100, Mauro Carvalho Chehab wrote:
> Sometimes, device drivers are bound into each other via try_module_get(),
> making such references invisible when looking at /proc/modules or lsmod.
> 
> Add a function to allow setting up module references for such
> cases, and call it when try_module_get() is used.
> 
> Reviewed-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
> ---
> 
> See [PATCH v2 0/2] at: https://lore.kernel.org/all/cover.1651314499.git.mchehab@kernel.org/
> 
>  include/linux/module.h |  4 +++-
>  kernel/module/main.c   | 35 +++++++++++++++++++++++++++++++++--
>  2 files changed, 36 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 46d4d5f2516e..836851baaad4 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -620,7 +620,9 @@ extern void __module_get(struct module *module);
>  
>  /* This is the Right Way to get a module: if it fails, it's being removed,
>   * so pretend it's not there. */
> -extern bool try_module_get(struct module *module);
> +extern bool __try_module_get(struct module *module, struct module *this);
> +
> +#define try_module_get(mod) __try_module_get(mod, THIS_MODULE)
>  
>  extern void module_put(struct module *module);
>  
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index 05a42d8fcd7a..9f4416381e65 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -631,6 +631,35 @@ static int ref_module(struct module *a, struct module *b)
>  	return 0;
>  }
>  
> +static int ref_module_dependency(struct module *mod,
> +				       struct module *this)

This can be on one line, right?

> +{
> +	int ret;
> +
> +	if (!this || !this->name) {
> +		return -EINVAL;
> +	}

Did you run checkpatch on this?  Please do :)

> +
> +	if (mod == this)
> +		return 0;

How can this happen?

When people mistakenly call try_module_get(THIS_MODULE)?  We should
throw up a big warning when that happens anyway as that's always wrong.

But that's a different issue from this change, sorry for the noise.

> +
> +	mutex_lock(&module_mutex);
> +
> +	ret = ref_module(this, mod);
> +
> +#ifdef CONFIG_MODULE_UNLOAD
> +	if (ret)
> +		goto ret;
> +
> +	ret = sysfs_create_link(mod->holders_dir,
> +				&this->mkobj.kobj, this->name);

Meta comment, why do we only create links if we can unload things?

thanks,

greg k-h