platform/x86: wmi: Fix notify callback locking

When an legacy WMI event handler is removed, an WMI event could
have called the handler just before it was removed, meaning the
handler could still be running after wmi_remove_notify_handler()
returns.
Something similar could also happens when using the WMI bus, as
the WMI core might still call the notify() callback from an WMI
driver even if its remove() callback was just called.

Fix this by introducing a rw semaphore which ensures that the
event state of a WMI device does not change while the WMI core
is handling an event for it.

Tested on a Dell Inspiron 3505 and a Acer Aspire E1-731.

Fixes: 1686f544 ("platform/x86: wmi: Incorporate acpi_install_notify_handler")
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20240103192707.115512-5-W_Armin@gmx.deSigned-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/platform/x86/wmi.c

@@ -25,6 +25,7 @@
 #include <linux/list.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>
+#include <linux/rwsem.h>
 #include <linux/slab.h>
 #include <linux/sysfs.h>
 #include <linux/types.h>
@@ -56,7 +57,6 @@ static_assert(__alignof__(struct guid_block) == 1);
 
 enum {	/* wmi_block flags */
 	WMI_READ_TAKES_NO_ARGS,
-	WMI_PROBED,
 };
 
 struct wmi_block {
@@ -64,8 +64,10 @@ struct wmi_block {
 	struct list_head list;
 	struct guid_block gblock;
 	struct acpi_device *acpi_device;
+	struct rw_semaphore notify_lock;	/* Protects notify callback add/remove */
 	wmi_notify_handler handler;
 	void *handler_data;
+	bool driver_ready;
 	unsigned long flags;
 };
 
@@ -603,6 +605,8 @@ acpi_status wmi_install_notify_handler(const char *guid,
 		return AE_ERROR;
 
 	wblock = container_of(wdev, struct wmi_block, dev);
+
+	down_write(&wblock->notify_lock);
 	if (wblock->handler) {
 		status = AE_ALREADY_ACQUIRED;
 	} else {
@@ -614,6 +618,7 @@ acpi_status wmi_install_notify_handler(const char *guid,
 
 		status = AE_OK;
 	}
+	up_write(&wblock->notify_lock);
 
 	wmi_device_put(wdev);
 
@@ -640,6 +645,8 @@ acpi_status wmi_remove_notify_handler(const char *guid)
 		return AE_ERROR;
 
 	wblock = container_of(wdev, struct wmi_block, dev);
+
+	down_write(&wblock->notify_lock);
 	if (!wblock->handler) {
 		status = AE_NULL_ENTRY;
 	} else {
@@ -651,6 +658,7 @@ acpi_status wmi_remove_notify_handler(const char *guid)
 
 		status = AE_OK;
 	}
+	up_write(&wblock->notify_lock);
 
 	wmi_device_put(wdev);
 
@@ -896,7 +904,9 @@ static int wmi_dev_probe(struct device *dev)
 		}
 	}
 
-	set_bit(WMI_PROBED, &wblock->flags);
+	down_write(&wblock->notify_lock);
+	wblock->driver_ready = true;
+	up_write(&wblock->notify_lock);
 
 	return 0;
 }
@@ -906,7 +916,9 @@ static void wmi_dev_remove(struct device *dev)
 	struct wmi_block *wblock = dev_to_wblock(dev);
 	struct wmi_driver *wdriver = drv_to_wdrv(dev->driver);
 
-	clear_bit(WMI_PROBED, &wblock->flags);
+	down_write(&wblock->notify_lock);
+	wblock->driver_ready = false;
+	up_write(&wblock->notify_lock);
 
 	if (wdriver->remove)
 		wdriver->remove(dev_to_wdev(dev));
@@ -1019,6 +1031,8 @@ static int wmi_create_device(struct device *wmi_bus_dev,
 		wblock->dev.setable = true;
 
  out_init:
+	init_rwsem(&wblock->notify_lock);
+	wblock->driver_ready = false;
 	wblock->dev.dev.bus = &wmi_bus_type;
 	wblock->dev.dev.parent = wmi_bus_dev;
 
@@ -1191,6 +1205,26 @@ acpi_wmi_ec_space_handler(u32 function, acpi_physical_address address,
 	}
 }
 
+static void wmi_notify_driver(struct wmi_block *wblock)
+{
+	struct wmi_driver *driver = drv_to_wdrv(wblock->dev.dev.driver);
+	struct acpi_buffer data = { ACPI_ALLOCATE_BUFFER, NULL };
+	acpi_status status;
+
+	if (!driver->no_notify_data) {
+		status = get_event_data(wblock, &data);
+		if (ACPI_FAILURE(status)) {
+			dev_warn(&wblock->dev.dev, "Failed to get event data\n");
+			return;
+		}
+	}
+
+	if (driver->notify)
+		driver->notify(&wblock->dev, data.pointer);
+
+	kfree(data.pointer);
+}
+
 static int wmi_notify_device(struct device *dev, void *data)
 {
 	struct wmi_block *wblock = dev_to_wblock(dev);
@@ -1199,28 +1233,17 @@ static int wmi_notify_device(struct device *dev, void *data)
 	if (!(wblock->gblock.flags & ACPI_WMI_EVENT && wblock->gblock.notify_id == *event))
 		return 0;
 
-	/* If a driver is bound, then notify the driver. */
-	if (test_bit(WMI_PROBED, &wblock->flags) && wblock->dev.dev.driver) {
-		struct wmi_driver *driver = drv_to_wdrv(wblock->dev.dev.driver);
-		struct acpi_buffer evdata = { ACPI_ALLOCATE_BUFFER, NULL };
-		acpi_status status;
-
-		if (!driver->no_notify_data) {
-			status = get_event_data(wblock, &evdata);
-			if (ACPI_FAILURE(status)) {
-				dev_warn(&wblock->dev.dev, "failed to get event data\n");
-				return -EIO;
-			}
-		}
-
-		if (driver->notify)
-			driver->notify(&wblock->dev, evdata.pointer);
-
-		kfree(evdata.pointer);
-	} else if (wblock->handler) {
-		/* Legacy handler */
-		wblock->handler(*event, wblock->handler_data);
+	down_read(&wblock->notify_lock);
+	/* The WMI driver notify handler conflicts with the legacy WMI handler.
+	 * Because of this the WMI driver notify handler takes precedence.
+	 */
+	if (wblock->dev.dev.driver && wblock->driver_ready) {
+		wmi_notify_driver(wblock);
+	} else {
+		if (wblock->handler)
+			wblock->handler(*event, wblock->handler_data);
 	}
+	up_read(&wblock->notify_lock);
 
 	acpi_bus_generate_netlink_event(wblock->acpi_device->pnp.device_class,
 					dev_name(&wblock->dev.dev), *event, 0);