linux-kernel - Re: [PATCH 1/5] debugobjects: Fix the misuse of global variables in fill

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Message-ID: <5cf23898-892c-c0a6-2525-206e21732665@huawei.com>
Date: Tue, 3 Sep 2024 19:14:42 +0800
From: "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To: Thomas Gleixner <tglx@...utronix.de>, Andrew Morton
	<akpm@...ux-foundation.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/5] debugobjects: Fix the misuse of global variables in
 fill_pool()



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

> 
> Thanks,
> 
>         tglx
> .
> 

-- 
Regards,
  Zhen Lei