rtc: rp5c01: fix possible race condition

[ Upstream commit bcdd559268 ]

The probe function is not allowed to fail after registering the RTC because
the following may happen:

CPU0:                                CPU1:
sys_load_module()
 do_init_module()
  do_one_initcall()
   cmos_do_probe()
    rtc_device_register()
     __register_chrdev()
     cdev->owner = struct module*
                                     open("/dev/rtc0")
    rtc_device_unregister()
  module_put()
  free_module()
   module_free(mod->module_core)
   /* struct module *module is now
      freed */
                                      chrdev_open()
                                       spin_lock(cdev_lock)
                                       cdev_get()
                                        try_module_get()
                                         module_is_live()
                                         /* dereferences already
                                            freed struct module* */

Switch to devm_rtc_allocate_device/rtc_register_device to register the rtc
as late as possible.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/rtc/rtc-rp5c01.c

@@ -249,16 +249,24 @@ static int __init rp5c01_rtc_probe(struct platform_device *dev)
 
 	platform_set_drvdata(dev, priv);
 
-	rtc = devm_rtc_device_register(&dev->dev, "rtc-rp5c01", &rp5c01_rtc_ops,
-				  THIS_MODULE);
+	rtc = devm_rtc_allocate_device(&dev->dev);
 	if (IS_ERR(rtc))
 		return PTR_ERR(rtc);
+
+	rtc->ops = &rp5c01_rtc_ops;
+
 	priv->rtc = rtc;
 
 	error = sysfs_create_bin_file(&dev->dev.kobj, &priv->nvram_attr);
 	if (error)
 		return error;
 
+	error = rtc_register_device(rtc);
+	if (error) {
+		sysfs_remove_bin_file(&dev->dev.kobj, &priv->nvram_attr);
+		return error;
+	}
+
 	return 0;
 }