Re: [PATCH v3 02/14] thermal: core: Rearrange checks in thermal_bind_cdev_to_trip()

Daniel Lezcano
2024-08-21T10:49:33Z

On 21/08/2024 11:44, lihuisong (C) wrote:
>
> 在 2024/8/21 17:28, Daniel Lezcano 写道:
>> On 21/08/2024 10:49, lihuisong (C) wrote:
>>
>> [ ... ]
>>
>>>> -    list_for_each_entry(pos2, &thermal_cdev_list, node) {
>>>> -        if (pos2 == cdev)
>>>> -            break;
>>>> -    }
>>>> +    lockdep_assert_held(&thermal_list_lock);
>>>> -    if (tz != pos1 || cdev != pos2)
>>>> +    if (list_empty(&tz->node) || list_empty(&cdev->node))
>>> The old verification is ensure that tz and cdev already add to
>>> thermal_tz_list and thermal_cdev_list，respectively.
>>> Namely, tz and cdev are definitely registered and intialized.
>>> The check is ok for all untizalized thermal_zone_device and cooling
>>> device.
>>> But the new verification doesn't seem to do that.
>>
>> If the tz or the cdev are registered then their "->node" is not empty
>> because they are linked with the thermal_list and cdev_list
>>
>> So either way is browsing the lists to find the tz/cdev or just check
>> "->node" is not empty. The latter the faster.
> Assume that tz/cdev isn't intiazlized and registered to thermal_tz_list
> or thermal_cdev_list. And then directly call this interface.

Then there is a bug in the internal code because the
thermal_zone_device_register*() and cooling_device_device_register()
allocate and initialize those structures.

The caller of the function is supposed to use the API provided by the
thermal framework. It is not possible to plan every stupid things a
driver can do. In this particular case, very likely the kernel will
crash immediately which is a sufficient test for me and coercive enough
to have the API user to put its code in question ;)

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