linux-kernel - [RFC] Revert "kernel/params.c: defer most of param_sysfs_init() to late

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Message-Id: <20250130225803.321004-1-shyamsaini@linux.microsoft.com>
Date: Thu, 30 Jan 2025 14:58:03 -0800
From: Shyam Saini <shyamsaini@...ux.microsoft.com>
To: linux-kernel@...r.kernel.org
Cc: linux@...musvillemoes.dk,
	mcgrof@...nel.org,
	code@...icks.com,
	okaya@...ux.microsoft.com,
	vijayb@...ux.microsoft.com
Subject: [RFC] Revert "kernel/params.c: defer most of param_sysfs_init() to late_initcall time"

This reverts commit 96a1a2412acba8c057c041833641d9b7dbf52170,
as it breaks the creation of /sys/module/<built-in-module>/drivers.

The reverted commit changed the initcall order for
param_sysfs_builtin() from subsys_initcall() to late_initcall(),
which impacts the module_kset list and its population.

Drivers which are initialized from subsys_initcall() or any other
higher precedence initcall couldn't find the related kobject entry
in the module_kset list because module_kset is not fully populated
at this point due to the reverted change. As a consequence,
module_add_driver() returns early without calling make_driver_name().
Therefore, /sys/module/<built-in-module>/drivers is never created.

This breaks user-space applications for eg: DPDK, which expect
/sys/module/vfio_pci/drivers/pci:vfio-pci/new_id to be present.

This revert restores the initcall order for param_sysfs_builtin()
and fixes the above mentioned issue.

Fixes: 96a1a2412acb ("kernel/params.c: defer most of param_sysfs_init() to late_initcall time")
Signed-off-by: Shyam Saini <shyamsaini@...ux.microsoft.com>
---
 kernel/params.c | 21 ++-------------------
 1 file changed, 2 insertions(+), 19 deletions(-)

diff --git a/kernel/params.c b/kernel/params.c
index 0074d29c9b80..890b44d36b1e 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -958,11 +958,7 @@ 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.
+ * param_sysfs_init - wrapper for built-in params support
  */
 static int __init param_sysfs_init(void)
 {
@@ -973,24 +969,11 @@ static int __init param_sysfs_init(void)
 		return -ENOMEM;
 	}

-	return 0;
-}
-subsys_initcall(param_sysfs_init);
-
-/*
- * param_sysfs_builtin_init - add sysfs version and parameter
- * attributes for built-in modules
- */
-static int __init param_sysfs_builtin_init(void)
-{
-	if (!module_kset)
-		return -ENOMEM;
-
 	version_sysfs_builtin();
 	param_sysfs_builtin();

 	return 0;
 }
-late_initcall(param_sysfs_builtin_init);
+subsys_initcall(param_sysfs_init);

 #endif /* CONFIG_SYSFS */
-- 
2.34.1