Re: [PATCH v8 4/8] PM / EM: add support for other devices than CPUs in Energy Model

[Lukasz Luba <lukasz.luba@arm.com>]

On 6/8/20 1:51 PM, Dan Carpenter wrote:
> On Mon, Jun 08, 2020 at 01:34:37PM +0100, Lukasz Luba wrote:
>> Hi Dan,
>>
>> Thank you for your analyzes.
>>
>> On 6/8/20 12:51 PM, Dan Carpenter wrote:
>>> Hi Lukasz,
>>>
>>> I love your patch! Perhaps something to improve:
>>>
>>> url:    https://github.com/0day-ci/linux/commits/Lukasz-Luba/Add-support-for-devices-in-the-Energy-Model/20200527-180614
>>> base:   https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git linux-next
>>>
>>> config: i386-randconfig-m021-20200605 (attached as .config)
>>> compiler: gcc-9 (Debian 9.3.0-13) 9.3.0
>>>
>>> If you fix the issue, kindly add following tag as appropriate
>>> Reported-by: kernel test robot <lkp@intel.com>
>>> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
>>>
>>> smatch warnings:
>>> kernel/power/energy_model.c:316 em_dev_register_perf_domain() error: we previously assumed 'dev->em_pd' could be null (see line 277)
>>>
>>> # https://github.com/0day-ci/linux/commit/110d050cb7ba1c96e63ada498979d1fd99529be2
>>> git remote add linux-review https://github.com/0day-ci/linux
>>> git remote update linux-review
>>> git checkout 110d050cb7ba1c96e63ada498979d1fd99529be2
>>> vim +316 kernel/power/energy_model.c
>>>
>>> 0e294e607adaf3 Lukasz Luba     2020-05-27  262  int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  263  				struct em_data_callback *cb, cpumask_t *cpus)
>>> 27871f7a8a341e Quentin Perret  2018-12-03  264  {
>>> 27871f7a8a341e Quentin Perret  2018-12-03  265  	unsigned long cap, prev_cap = 0;
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  266  	int cpu, ret;
>>> 27871f7a8a341e Quentin Perret  2018-12-03  267
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  268  	if (!dev || !nr_states || !cb)
>>> 27871f7a8a341e Quentin Perret  2018-12-03  269  		return -EINVAL;
>>> 27871f7a8a341e Quentin Perret  2018-12-03  270
>>> 27871f7a8a341e Quentin Perret  2018-12-03  271  	/*
>>> 27871f7a8a341e Quentin Perret  2018-12-03  272  	 * Use a mutex to serialize the registration of performance domains and
>>> 27871f7a8a341e Quentin Perret  2018-12-03  273  	 * let the driver-defined callback functions sleep.
>>> 27871f7a8a341e Quentin Perret  2018-12-03  274  	 */
>>> 27871f7a8a341e Quentin Perret  2018-12-03  275  	mutex_lock(&em_pd_mutex);
>>> 27871f7a8a341e Quentin Perret  2018-12-03  276
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27 @277  	if (dev->em_pd) {
>>>                                                               ^^^^^^^^^^
>>> Check for NULL.
>>>
>>> 27871f7a8a341e Quentin Perret  2018-12-03  278  		ret = -EEXIST;
>>> 27871f7a8a341e Quentin Perret  2018-12-03  279  		goto unlock;
>>> 27871f7a8a341e Quentin Perret  2018-12-03  280  	}
>>> 27871f7a8a341e Quentin Perret  2018-12-03  281
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  282  	if (_is_cpu_device(dev)) {
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  283  		if (!cpus) {
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  284  			dev_err(dev, "EM: invalid CPU mask\n");
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  285  			ret = -EINVAL;
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  286  			goto unlock;
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  287  		}
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  288
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  289  		for_each_cpu(cpu, cpus) {
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  290  			if (em_cpu_get(cpu)) {
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  291  				dev_err(dev, "EM: exists for CPU%d\n", cpu);
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  292  				ret = -EEXIST;
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  293  				goto unlock;
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  294  			}
>>> 27871f7a8a341e Quentin Perret  2018-12-03  295  			/*
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  296  			 * All CPUs of a domain must have the same
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  297  			 * micro-architecture since they all share the same
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  298  			 * table.
>>> 27871f7a8a341e Quentin Perret  2018-12-03  299  			 */
>>> 8ec59c0f5f4966 Vincent Guittot 2019-06-17  300  			cap = arch_scale_cpu_capacity(cpu);
>>> 27871f7a8a341e Quentin Perret  2018-12-03  301  			if (prev_cap && prev_cap != cap) {
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  302  				dev_err(dev, "EM: CPUs of %*pbl must have the same capacity\n",
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  303  					cpumask_pr_args(cpus));
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  304
>>> 27871f7a8a341e Quentin Perret  2018-12-03  305  				ret = -EINVAL;
>>> 27871f7a8a341e Quentin Perret  2018-12-03  306  				goto unlock;
>>> 27871f7a8a341e Quentin Perret  2018-12-03  307  			}
>>> 27871f7a8a341e Quentin Perret  2018-12-03  308  			prev_cap = cap;
>>> 27871f7a8a341e Quentin Perret  2018-12-03  309  		}
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  310  	}
>>> 27871f7a8a341e Quentin Perret  2018-12-03  311
>>> 110d050cb7ba1c Lukasz Luba     2020-05-27  312  	ret = em_create_pd(dev, nr_states, cb, cpus);
>>>
>>>
>>> If it's a _is_cpu_device() then it iterates through a bunch of devices
>>> and sets up cpu_dev->em_pd for each.  Presumably one of the devices is
>>> "dev" or this would crash pretty early on in testing?
>>
>> Yes, all of the devices taken from 'cpus' mask will get the em_pd set
>> including the suspected @dev.
>> To calm down this static analyzer I can remove the 'else'
>> in line 204 to make 'dev->em_pd = pd' set always.
>> 199         if (_is_cpu_device(dev))
>> 200                 for_each_cpu(cpu, cpus) {
>> 201                         cpu_dev = get_cpu_device(cpu);
>> 202                         cpu_dev->em_pd = pd;
>> 203                 }
>> 204         else
>> 205                 dev->em_pd = pd;
>>
>>
>> Do you think it's a good solution and will work for this tool?
> 
> It's not about the tool...  Ignore the tool when it's wrong.  But I do
> think the code is slightly more clear without the else statement.
> 
> Arguments could be made either way.  Removing the else statement means
> we set dev->em_pd twice...  But I *personally* lean vaguely towards
> removing the else statement.  :P

Thanks, I will remove the else statement and add your 'Reported-by'

Regards,
Lukasz

> 
> That would make the warning go away as well.
> 
> regards,
> dan carpenter
>