Re: [PATCH 1/5] debugobjects: Fix the misuse of global variables in fill_pool()

[Leizhen (ThunderTown)]

On 2024/9/3 19:43, Thomas Gleixner wrote:
> On Tue, Sep 03 2024 at 19:14, Leizhen wrote:
>> On 2024/9/3 17:37, Thomas Gleixner wrote:
>>> On Tue, Sep 03 2024 at 15:00, Leizhen wrote:
>>>>>> @@ -84,10 +85,7 @@ static int __data_racy                       debug_objects_fixups __read_mostly;
>>>>>>  static int __data_racy                 debug_objects_warnings __read_mostly;
>>>>>>  static int __data_racy                 debug_objects_enabled __read_mostly
>>>>>>                                         = CONFIG_DEBUG_OBJECTS_ENABLE_DEFAULT;
>>>>>> -static int __data_racy                 debug_objects_pool_size __read_mostly
>>>>>> -                                       = ODEBUG_POOL_SIZE;
>>>>>> -static int __data_racy                 debug_objects_pool_min_level __read_mostly
>>>>>> -                                       = ODEBUG_POOL_MIN_LEVEL;
>>>>>> +static int __data_racy                 obj_pool_min_free = ODEBUG_POOL_SIZE;
>>>>
>>>> Sorry, I rechecked it again. After this patch, obj_pool_min_free is referenced in the
>>>> same way as obj_pool_max_used. The only race point is located in debug_stats_show().
>>>> However, this reference point does not need to be included in the race analysis. So
>>>> there is no need to add __data_racy for obj_pool_min_free.
>>>
>>> The read races against the write, so KCSAN can detect it and complain, no?
>>
>> Oh, I just saw that there were a lot of other global variables in that function
>> that didn't mask KCSAN's detection. So I'll recheck each global variable.
>> However, for obj_pool_min_free, it seems that it would be better to just add
>> READ_ONCE() in debug_stats_show(). This does not prevent the compiler from
>> optimizing variable references in the lock.
>>
>> # define __data_racy volatile
> 
> This is only when KCSAN is enabled. Otherwise it's empty.
> 
> And if you do a READ_ONCE() then you need a corresponding WRITE_ONCE()
> to make sense. __data_racy is much simpler for that.

OK, I will use __data_racy, thanks

> 
> Thanks,
> 
>         tglx
> .
> 

-- 
Regards,
  Zhen Lei