On Mon, 21 May 2018, Uwe Kleine-König wrote: > > The race looks like that (thanks Jiri): > > > > 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* */ > > [Context: For a patch to rtc-pcf2127.c Alexandre Belloni asked not to > fail after rtc_device_register successfully finished and pointed to this > reasoning as explaination.] > > If there is really such a race then (I hope) there is > something in the cdev code that needs fixing. According to my > understanding, when rtc_device_unregister returned, the cdev is gone and > so chrdev_open is supposed to fail.
Oh wow, hello back to 4 years ago! Looking at the current code, I don't think there is no such race any more, as the last thing cmos_do_probe() -> __rtc_register_device() does that can potentially fail is the chardev creation itself. IOW if it exists, it's guaranteed to not go away on a probe error handling path (and the rest is protected via ops_lock mutex). -- Jiri Kosina SUSE Labs