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

[Zhiqiang Liu <liuzhiqiang26@huawei.com>]

From: Zhiqiang Liu <liuzhiqiang26@huawei.com>

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")
Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
---
 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;
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(ref_module);
-- 
2.19.1