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

[Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>]

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@xxxxxxxxx>
Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
---

See [PATCH v2 0/2] at: https://lore.kernel.org/all/cover.1651314499.git.mchehab@xxxxxxxxxx/

 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)
+{
+	int ret;
+
+	if (!this || !this->name) {
+		return -EINVAL;
+	}
+
+	if (mod == this)
+		return 0;
+
+	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);
+#endif
+
+ret:
+	mutex_unlock(&module_mutex);
+	return ret;
+}
+
 /* Clear the unload stuff of the module. */
 static void module_unload_free(struct module *mod)
 {
@@ -841,7 +870,7 @@ void __module_get(struct module *module)
 }
 EXPORT_SYMBOL(__module_get);
 
-bool try_module_get(struct module *module)
+bool __try_module_get(struct module *module, struct module *this)
 {
 	bool ret = true;
 
@@ -856,9 +885,11 @@ bool try_module_get(struct module *module)
 
 		preempt_enable();
 	}
+	if (ret)
+		ref_module_dependency(module, this);
 	return ret;
 }
-EXPORT_SYMBOL(try_module_get);
+EXPORT_SYMBOL(__try_module_get);
 
 void module_put(struct module *module)
 {
-- 
2.35.1