Re: [PATCH] module: add usage links when calling ref_module func

[Jessica Yu]

+++ Zhiqiang Liu [28/06/19 20:32 +0800]:
> From: Zhiqiang Liu <liuzhiqiang26@xxxxxxxxxx>
>
> Problem: Users can call ref_module func in their modules to construct
> relationships with other modules. However, the holders
> '/sys/module/<mod-name>/holders' of the target module donot include
> the users` module. So lsmod command misses detailed info of 'Used by'.
>
> When load module, the process is given as follows,
> load_module()
> 	-> mod_sysfs_setup()
> 		-> add_usage_links
> 	-> do_init_module
> 		-> mod->init()
>
> add_usage_links func creates holders of target modules linking to
> this module. If ref_module is called in mod->init() func, the usage
> links cannot be added.
>
> Here, we will add usage link of a to b's holder_dir.
>
> Fixes: 9bea7f239 ("module: fix bne2 "gave up waiting for init of module libcrc32c")

I think we can drop this tag; it doesn't fix a bug specifically
introduced by that particular commit.

> Signed-off-by: Zhiqiang Liu <liuzhiqiang26@xxxxxxxxxx>
> ---
> kernel/module.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/kernel/module.c b/kernel/module.c
> index 80c7c09584cf..11c6aff37b1f 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -871,6 +871,11 @@ int ref_module(struct module *a, struct module *b)
> 		module_put(b);
> 		return err;
> 	}
> +
> +	err = sysfs_create_link(b->holders_dir, &a->mkobj.kobj, a->name);
> +	if (err)
> +		return err;

We need to fix the error handling here - the module_use struct
allocated in the call to add_module_usage() needs to be freed (you
could just modify add_module_usage() to return the use pointer so that
it's easier to free from within ref_module()), module_put() needs to
be called, and the use struct should be removed from its respective
lists (see module_unload_free()).

Thanks,

Jessica