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

Lukasz Luba
2020-06-08T12:34:45Z

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?

Regards,
Lukasz

>
> 110d050cb7ba1c Lukasz Luba 2020-05-27 313 if (ret)
> 27871f7a8a341e Quentin Perret 2018-12-03 314 goto unlock;
> 27871f7a8a341e Quentin Perret 2018-12-03 315
> 110d050cb7ba1c Lukasz Luba 2020-05-27 @316 em_debug_create_pd(dev);
> ^^^
> Dereferences dev->em_pd.
>
> 110d050cb7ba1c Lukasz Luba 2020-05-27 317 dev_info(dev, "EM: created perf domain\n");
> 27871f7a8a341e Quentin Perret 2018-12-03 318
> 27871f7a8a341e Quentin Perret 2018-12-03 319 unlock:
> 27871f7a8a341e Quentin Perret 2018-12-03 320 mutex_unlock(&em_pd_mutex);
> 27871f7a8a341e Quentin Perret 2018-12-03 321 return ret;
> 27871f7a8a341e Quentin Perret 2018-12-03 322 }
> 0e294e607adaf3 Lukasz Luba 2020-05-27 323 EXPORT_SYMBOL_GPL(em_dev_register_perf_domain);
>
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
>