On Friday, December 29, 2017 7:45:22 PM CET gaurav jindal wrote: > On Wed, Dec 27, 2017 at 03:30:02AM +0100, Rafael J. Wysocki wrote: > > On Wed, Dec 27, 2017 at 2:57 AM, gaurav jindal > > <gauravjindal1...@gmail.com> wrote: > > > On Wed, Dec 27, 2017 at 01:42:58AM +0100, Rafael J. Wysocki wrote: > > >> On Tue, Dec 26, 2017 at 8:26 AM, gaurav jindal > > >> <gauravjindal1...@gmail.com> wrote: > > >> > When selecting the idle state using cpuidle_select, there is no > > >> > check on cpuidle_curr_governor. In cpuidle_switch_governor, > > >> > cpuidle_currr_governor can be set to NULL to specify "disabled". > > >> > > >> How exactly? > > > > > > In cpuidle_switch_governor: > > > > > > /** > > > * cpuidle_switch_governor - changes the governor > > > * @gov: the new target governor > > > * > > > * NOTE: "gov" can be NULL to specify disabled > > > * Must be called with cpuidle_lock acquired. > > > */ > > > int cpuidle_switch_governor(struct cpuidle_governor *gov) > > > { > > > struct cpuidle_device *dev; > > > > > > if (gov == cpuidle_curr_governor) > > > return 0; > > > > > > cpuidle_uninstall_idle_handler(); > > > > > > if (cpuidle_curr_governor) { > > > list_for_each_entry(dev, &cpuidle_detected_devices, > > > device_list) > > > cpuidle_disable_device(dev); > > > } > > > > > > cpuidle_curr_governor = gov; > > > > > > This allows to set the cpuidle_switch_governor as NULL. Although there is > > > no > > > current code flow leading here, but it has a potential for bug in future. > > > So > > > may be better to have prevention. > > > > Or maybe not. > > > > Why don't you make cpuidle_switch_governor() check the argument > > against NULL instead? > > If we check gov (argument passed in cpuidle_switch_governor())against > NULL in cpuidle_switch_governor, can be a problem in a case where it > is called as > cpuidle_switch_governor(NULL); > > If cpuidle_curr_governor is not NULL, first the device is disabled. > > if (cpuidle_curr_governor) { > list_for_each_entry(dev, &cpuidle_detected_devices, device_list) > cpuidle_disable_device(dev); > } > > after this cpuidle_curr_governor is set to gov, which is NULL in this case. > > cpuidle_curr_governor = gov; > /* if is not updated by inserting a check, it will have an oudated value*/ > > Now, if gov is not NULL (which it is in this case), cpuidle device is enabled > > if (gov) { > list_for_each_entry(dev, &cpuidle_detected_devices, device_list) > cpuidle_enable_device(dev); > cpuidle_install_idle_handler(); > printk(KERN_INFO "cpuidle: using governor %s\n", gov->name); > } > If we check for gov against NULL in this function, it will produce > dangling pointers and resource leaks.
I didn't recommend you to introduce bugs. Just return -EINVAL if gov is NULL before checking if gov is equal to cpuidle_curr_governor. Thanks, Rafael