rtc: rk808: fix possible race condition

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>

diff --git a/drivers/rtc/rtc-rk808.c b/drivers/rtc/rtc-rk808.c
index e40f35d..739c0d4 100644 (file)
--- a/drivers/rtc/rtc-rk808.c
+++ b/drivers/rtc/rtc-rk808.c
@@ -405,12 +405,11 @@ static int rk808_rtc_probe(struct platform_device *pdev)
 
        device_init_wakeup(&pdev->dev, 1);
 
-       rk808_rtc->rtc = devm_rtc_device_register(&pdev->dev, "rk808-rtc",
-                                                 &rk808_rtc_ops, THIS_MODULE);
-       if (IS_ERR(rk808_rtc->rtc)) {
-               ret = PTR_ERR(rk808_rtc->rtc);
-               return ret;
-       }
+       rk808_rtc->rtc = devm_rtc_allocate_device(&pdev->dev);
+       if (IS_ERR(rk808_rtc->rtc))
+               return PTR_ERR(rk808_rtc->rtc);
+
+       rk808_rtc->rtc->ops = &rk808_rtc_ops;
 
        rk808_rtc->irq = platform_get_irq(pdev, 0);
        if (rk808_rtc->irq < 0) {
@@ -427,9 +426,10 @@ static int rk808_rtc_probe(struct platform_device *pdev)
        if (ret) {
                dev_err(&pdev->dev, "Failed to request alarm IRQ %d: %d\n",
                        rk808_rtc->irq, ret);
+               return ret;
        }
 
-       return ret;
+       return rtc_register_device(rk808_rtc->rtc);
 }
 
 static struct platform_driver rk808_rtc_driver = {