[PATCH v4 1/4] kernel: param: initialize module_kset before do_initcalls()

[Shashank Balaji]

module_kset is initialized in param_sysfs_init(), a subsys_initcall. A number
of platform drivers register themselves prior to subsys_initcalls
(tegra194_cbb_driver registers in a pure_initcall, for example). With an
upcoming patch ("driver core: platform: set mod_name in driver registration")
that sets their mod_name in struct device_driver, lookup_or_create_module_kobject()
will be called for those drivers, which calls kset_find_obj(module_kset, mod_name).
This causes a null deref because module_kset isn't alive yet.

Fix this by initializing module_kset in do_basic_setup() before do_initcalls().
Modernize the pr_warn while we're at it.

Suggested-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Suggested-by: Gary Guo <gary at garyguo.net>
Co-developed-by: Rahul Bukte <rahul.bukte at sony.com>
Signed-off-by: Rahul Bukte <rahul.bukte at sony.com>
Signed-off-by: Shashank Balaji <shashank.mahadasyam at sony.com>
---
 include/linux/module.h |  4 ++++
 init/main.c            |  1 +
 kernel/params.c        | 21 +++++++++------------
 3 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/include/linux/module.h b/include/linux/module.h
index 7566815fabbe..6478596e8f9f 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -886,6 +886,10 @@ static inline void module_for_each_mod(int(*func)(struct module *mod, void *data
 #ifdef CONFIG_SYSFS
 extern struct kset *module_kset;
 extern const struct kobj_type module_ktype;
+
+void param_sysfs_init(void);
+#else
+static inline void param_sysfs_init(void) {}
 #endif /* CONFIG_SYSFS */
 
 #define symbol_request(x) try_then_request_module(symbol_get(x), "symbol:" #x)
diff --git a/init/main.c b/init/main.c
index 96f93bb06c49..01552c6b62ff 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1486,6 +1486,7 @@ static void __init do_basic_setup(void)
 	ksysfs_init();
 	driver_init();
 	init_irq_proc();
+	param_sysfs_init();
 	do_ctors();
 	do_initcalls();
 }
diff --git a/kernel/params.c b/kernel/params.c
index 74d620bc2521..d1e3934fb3a7 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -942,22 +942,19 @@ const struct kobj_type module_ktype = {
 /*
  * param_sysfs_init - create "module" kset
  *
- * This must be done before the initramfs is unpacked and
- * request_module() thus becomes possible, because otherwise the
- * module load would fail in mod_sysfs_init.
+ * Must run before:
+ * - do_initcalls(): some drivers register during initcalls and rely on
+ *   module_kset existing for their sysfs module symlink.
+ * - rootfs_initcall (initramfs unpack): request_module() becomes possible.
+ *   But if module_kset is null, module load would fail in mod_sysfs_init(),
+ *   causing request_module() to fail.
  */
-static int __init param_sysfs_init(void)
+void __init param_sysfs_init(void)
 {
 	module_kset = kset_create_and_add("module", &module_uevent_ops, NULL);
-	if (!module_kset) {
-		printk(KERN_WARNING "%s (%d): error creating kset\n",
-			__FILE__, __LINE__);
-		return -ENOMEM;
-	}
-
-	return 0;
+	if (!module_kset)
+		pr_warn("Error creating module kset\n");
 }
-subsys_initcall(param_sysfs_init);
 
 /*
  * param_sysfs_builtin_init - add sysfs version and parameter

-- 
2.43.0