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

From: Jessica Yu
Date: Mon Jul 01 2019 - 09:56:08 EST

+++ 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,
-> 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)
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()).