Messages in this thread Patch in this message | | | Date | Thu, 4 Jan 2018 23:39:07 +0530 | From | gaurav jindal <> | Subject | Re: [PATCH]cpuidle: preventive check in cpuidle_select against crash |
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On Wed, Jan 03, 2018 at 12:16:26PM +0100, Rafael J. Wysocki wrote: > 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 > > > <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. > > I didn't recommend you to introduce bugs. > I did not intend to do so. I am really sorry it got expressed in that way :(. > Just return -EINVAL if gov is NULL before checking if gov is equal to > cpuidle_curr_governor. > Okay > Thanks, > Rafael >
this patch checks if the new governor is NULL before updating the cupidle_curr_governor.
Signed-off-by: gaurav jindal<gauravjindal1104@gmail.com>
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diff --git a/drivers/cpuidle/governor.c b/drivers/cpuidle/governor.c index 4e78263..5d359af 100644 --- a/drivers/cpuidle/governor.c +++ b/drivers/cpuidle/governor.c @@ -36,14 +36,15 @@ static struct cpuidle_governor * __cpuidle_find_governor(const char *str) /** * 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) + return -EINVAL; + if (gov == cpuidle_curr_governor) return 0;
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