Messages in this thread | | | Date | Sat, 30 Dec 2017 00:15:22 +0530 | From | gaurav jindal <> | Subject | Re: [PATCH]cpuidle: preventive check in cpuidle_select against crash |
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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 > <gauravjindal1104@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 > >> <gauravjindal1104@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.
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