staging: pi433: fix memory leak with using debugfs_lookup()

When calling debugfs_lookup() the result must have dput() called on it,
otherwise the memory will leak over time.  To make things simpler, just
call debugfs_lookup_and_remove() instead which handles all of the logic
at once.  This requires saving off the root directory dentry to make
creation of individual device subdirectories easier.

Cc: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>
Cc: Dan Carpenter <error27@gmail.com>
Cc: Sidong Yang <realwakka@gmail.com>
Cc: Liu Shixin <liushixin2@huawei.com>
Cc: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20230202141138.2291946-1-gregkh@linuxfoundation.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/pi433/pi433_if.c

@@ -55,6 +55,7 @@
 static dev_t pi433_dev;
 static DEFINE_IDR(pi433_idr);
 static DEFINE_MUTEX(minor_lock); /* Protect idr accesses */
+static struct dentry *root_dir;	/* debugfs root directory for the driver */
 
 static struct class *pi433_class; /* mainly for udev to create /dev/pi433 */
 
@@ -1306,8 +1307,7 @@ static int pi433_probe(struct spi_device *spi)
 	/* spi setup */
 	spi_set_drvdata(spi, device);
 
-	entry = debugfs_create_dir(dev_name(device->dev),
-				   debugfs_lookup(KBUILD_MODNAME, NULL));
+	entry = debugfs_create_dir(dev_name(device->dev), root_dir);
 	debugfs_create_file("regs", 0400, entry, device, &pi433_debugfs_regs_fops);
 
 	return 0;
@@ -1333,9 +1333,8 @@ static int pi433_probe(struct spi_device *spi)
 static void pi433_remove(struct spi_device *spi)
 {
 	struct pi433_device	*device = spi_get_drvdata(spi);
-	struct dentry *mod_entry = debugfs_lookup(KBUILD_MODNAME, NULL);
 
-	debugfs_remove(debugfs_lookup(dev_name(device->dev), mod_entry));
+	debugfs_lookup_and_remove(dev_name(device->dev), root_dir);
 
 	/* free GPIOs */
 	free_gpio(device);
@@ -1408,7 +1407,7 @@ static int __init pi433_init(void)
 		return PTR_ERR(pi433_class);
 	}
 
-	debugfs_create_dir(KBUILD_MODNAME, NULL);
+	root_dir = debugfs_create_dir(KBUILD_MODNAME, NULL);
 
 	status = spi_register_driver(&pi433_spi_driver);
 	if (status < 0) {
@@ -1427,7 +1426,7 @@ static void __exit pi433_exit(void)
 	spi_unregister_driver(&pi433_spi_driver);
 	class_destroy(pi433_class);
 	unregister_chrdev(MAJOR(pi433_dev), pi433_spi_driver.driver.name);
-	debugfs_remove_recursive(debugfs_lookup(KBUILD_MODNAME, NULL));
+	debugfs_remove(root_dir);
 }
 module_exit(pi433_exit);