rtc: cmos: fix possible race condition
authorAlexandre Belloni <alexandre.belloni@bootlin.com>
Mon, 12 Feb 2018 22:47:45 +0000 (23:47 +0100)
committerAlexandre Belloni <alexandre.belloni@bootlin.com>
Thu, 1 Mar 2018 09:49:29 +0000 (10:49 +0100)
commit53d29e0a3afe0567db9e4360e8523b092eb2d4e4
treedacc451b5910022aae5fb25acf00a59672f6d19f
parent1af7068d2a19d333e9280f8a43bc7215c90bfb91
rtc: cmos: 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>
drivers/rtc/rtc-cmos.c