PCI: hotplug: Embed hotplug_slot

When the PCI hotplug core and its first user, cpqphp, were introduced in
February 2002 with historic commit a8a2069f432c, cpqphp allocated a slot
struct for its internal use plus a hotplug_slot struct to be registered
with the hotplug core and linked the two with pointers:
https://git.kernel.org/tglx/history/c/a8a2069f432c

Nowadays, the predominant pattern in the tree is to embed ("subclass")
such structures in one another and cast to the containing struct with
container_of().  But it wasn't until July 2002 that container_of() was
introduced with historic commit ec4f214232cf:
https://git.kernel.org/tglx/history/c/ec4f214232cf

pnv_php, introduced in 2016, did the right thing and embedded struct
hotplug_slot in its internal struct pnv_php_slot, but all other drivers
cargo-culted cpqphp's design and linked separate structs with pointers.

Embedding structs is preferrable to linking them with pointers because
it requires fewer allocations, thereby reducing overhead and simplifying
error paths.  Casting an embedded struct to the containing struct
becomes a cheap subtraction rather than a dereference.  And having fewer
pointers reduces the risk of them pointing nowhere either accidentally
or due to an attack.

Convert all drivers to embed struct hotplug_slot in their internal slot
struct.  The "private" pointer in struct hotplug_slot thereby becomes
unused, so drop it.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>  # drivers/pci/hotplug/rpa*
Acked-by: Sebastian Ott <sebott@linux.ibm.com>        # drivers/pci/hotplug/s390*
Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com> # drivers/platform/x86
Cc: Len Brown <lenb@kernel.org>
Cc: Scott Murray <scott@spiteful.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Oliver OHalloran <oliveroh@au1.ibm.com>
Cc: Gavin Shan <gwshan@linux.vnet.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: Corentin Chary <corentin.chary@gmail.com>
Cc: Darren Hart <dvhart@infradead.org>

2 files changed, 21 insertions, 35 deletions

diff --git a/drivers/platform/x86/asus-wmi.c b/drivers/platform/x86/asus-wmi.c
index 019b037319e3..93ee2d5466f8 100644
--- a/drivers/platform/x86/asus-wmi.c
+++ b/drivers/platform/x86/asus-wmi.c
@@ -254,7 +254,7 @@ struct asus_wmi {
 	int asus_hwmon_num_fans;
 	int asus_hwmon_pwm;
 
-	struct hotplug_slot *hotplug_slot;
+	struct hotplug_slot hotplug_slot;
 	struct mutex hotplug_lock;
 	struct mutex wmi_lock;
 	struct workqueue_struct *hotplug_workqueue;
@@ -753,7 +753,7 @@ static void asus_rfkill_hotplug(struct asus_wmi *asus)
 	if (asus->wlan.rfkill)
 		rfkill_set_sw_state(asus->wlan.rfkill, blocked);
 
-	if (asus->hotplug_slot) {
+	if (asus->hotplug_slot.ops) {
 		bus = pci_find_bus(0, 1);
 		if (!bus) {
 			pr_warn("Unable to find PCI bus 1?\n");
@@ -858,7 +858,8 @@ static void asus_unregister_rfkill_notifier(struct asus_wmi *asus, char *node)
 static int asus_get_adapter_status(struct hotplug_slot *hotplug_slot,
 				   u8 *value)
 {
-	struct asus_wmi *asus = hotplug_slot->private;
+	struct asus_wmi *asus = container_of(hotplug_slot,
+					     struct asus_wmi, hotplug_slot);
 	int result = asus_wmi_get_devstate_simple(asus, ASUS_WMI_DEVID_WLAN);
 
 	if (result < 0)
@@ -898,14 +899,9 @@ static int asus_setup_pci_hotplug(struct asus_wmi *asus)
 
 	INIT_WORK(&asus->hotplug_work, asus_hotplug_work);
 
-	asus->hotplug_slot = kzalloc(sizeof(struct hotplug_slot), GFP_KERNEL);
-	if (!asus->hotplug_slot)
-		goto error_slot;
+	asus->hotplug_slot.ops = &asus_hotplug_slot_ops;
 
-	asus->hotplug_slot->private = asus;
-	asus->hotplug_slot->ops = &asus_hotplug_slot_ops;
-
-	ret = pci_hp_register(asus->hotplug_slot, bus, 0, "asus-wifi");
+	ret = pci_hp_register(&asus->hotplug_slot, bus, 0, "asus-wifi");
 	if (ret) {
 		pr_err("Unable to register hotplug slot - %d\n", ret);
 		goto error_register;
@@ -914,9 +910,7 @@ static int asus_setup_pci_hotplug(struct asus_wmi *asus)
 	return 0;
 
 error_register:
-	kfree(asus->hotplug_slot);
-	asus->hotplug_slot = NULL;
-error_slot:
+	asus->hotplug_slot.ops = NULL;
 	destroy_workqueue(asus->hotplug_workqueue);
 error_workqueue:
 	return ret;
@@ -1044,10 +1038,8 @@ static void asus_wmi_rfkill_exit(struct asus_wmi *asus)
 	 * asus_unregister_rfkill_notifier()
 	 */
 	asus_rfkill_hotplug(asus);
-	if (asus->hotplug_slot) {
-		pci_hp_deregister(asus->hotplug_slot);
-		kfree(asus->hotplug_slot);
-	}
+	if (asus->hotplug_slot.ops)
+		pci_hp_deregister(&asus->hotplug_slot);
 	if (asus->hotplug_workqueue)
 		destroy_workqueue(asus->hotplug_workqueue);
 
diff --git a/drivers/platform/x86/eeepc-laptop.c b/drivers/platform/x86/eeepc-laptop.c
index 028b20f82962..e6946a9beb5a 100644
--- a/drivers/platform/x86/eeepc-laptop.c
+++ b/drivers/platform/x86/eeepc-laptop.c
@@ -177,7 +177,7 @@ struct eeepc_laptop {
 	struct rfkill *wwan3g_rfkill;
 	struct rfkill *wimax_rfkill;
 
-	struct hotplug_slot *hotplug_slot;
+	struct hotplug_slot hotplug_slot;
 	struct mutex hotplug_lock;
 
 	struct led_classdev tpd_led;
@@ -582,7 +582,7 @@ static void eeepc_rfkill_hotplug(struct eeepc_laptop *eeepc, acpi_handle handle)
 	mutex_lock(&eeepc->hotplug_lock);
 	pci_lock_rescan_remove();
 
-	if (!eeepc->hotplug_slot)
+	if (!eeepc->hotplug_slot.ops)
 		goto out_unlock;
 
 	port = acpi_get_pci_dev(handle);
@@ -715,8 +715,11 @@ static void eeepc_unregister_rfkill_notifier(struct eeepc_laptop *eeepc,
 static int eeepc_get_adapter_status(struct hotplug_slot *hotplug_slot,
 				    u8 *value)
 {
-	struct eeepc_laptop *eeepc = hotplug_slot->private;
-	int val = get_acpi(eeepc, CM_ASL_WLAN);
+	struct eeepc_laptop *eeepc;
+	int val;
+
+	eeepc = container_of(hotplug_slot, struct eeepc_laptop, hotplug_slot);
+	val = get_acpi(eeepc, CM_ASL_WLAN);
 
 	if (val == 1 || val == 0)
 		*value = val;
@@ -741,14 +744,9 @@ static int eeepc_setup_pci_hotplug(struct eeepc_laptop *eeepc)
 		return -ENODEV;
 	}
 
-	eeepc->hotplug_slot = kzalloc(sizeof(struct hotplug_slot), GFP_KERNEL);
-	if (!eeepc->hotplug_slot)
-		goto error_slot;
+	eeepc->hotplug_slot.ops = &eeepc_hotplug_slot_ops;
 
-	eeepc->hotplug_slot->private = eeepc;
-	eeepc->hotplug_slot->ops = &eeepc_hotplug_slot_ops;
-
-	ret = pci_hp_register(eeepc->hotplug_slot, bus, 0, "eeepc-wifi");
+	ret = pci_hp_register(&eeepc->hotplug_slot, bus, 0, "eeepc-wifi");
 	if (ret) {
 		pr_err("Unable to register hotplug slot - %d\n", ret);
 		goto error_register;
@@ -757,9 +755,7 @@ static int eeepc_setup_pci_hotplug(struct eeepc_laptop *eeepc)
 	return 0;
 
 error_register:
-	kfree(eeepc->hotplug_slot);
-	eeepc->hotplug_slot = NULL;
-error_slot:
+	eeepc->hotplug_slot.ops = NULL;
 	return ret;
 }
 
@@ -820,10 +816,8 @@ static void eeepc_rfkill_exit(struct eeepc_laptop *eeepc)
 		eeepc->wlan_rfkill = NULL;
 	}
 
-	if (eeepc->hotplug_slot) {
-		pci_hp_deregister(eeepc->hotplug_slot);
-		kfree(eeepc->hotplug_slot);
-	}
+	if (eeepc->hotplug_slot.ops)
+		pci_hp_deregister(&eeepc->hotplug_slot);
 
 	if (eeepc->bluetooth_rfkill) {
 		rfkill_unregister(eeepc->bluetooth_rfkill);