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

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Message-ID: <3bb35c94-dd54-33d4-b7ac-64f0d2b77c07@huawei.com>
Date: Tue, 3 Sep 2024 11:22:51 +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 10:16, Leizhen (ThunderTown) wrote:
> 
> 
> On 2024/9/3 0:22, Thomas Gleixner wrote:
>> On Mon, Sep 02 2024 at 22:05, Zhen Lei wrote:
>>
>>> The global variable 'obj_pool_min_free' records the lowest historical
>>> value of the number of nodes in the global list 'obj_pool', instead of
>>> being used as the lowest threshold value. This may be a mistake and
>>
>> Maybe? It's either a bug or not.
> 
> Yes, it's a bug, but I'm just learning this module, so I'm not confident.
> 
>>
>>> should be replaced with variable 'debug_objects_pool_min_level'.
>>
>> And if it's a bug then it has to be replaced.
> 
> OK, I will update the commit message in V2.
> 
>>
>> This misses another minor issue:
>>
>> static int			obj_pool_min_free = ODEBUG_POOL_SIZE;
>>
>> static int  __data_racy		debug_objects_pool_min_level __read_mostly
>> 				= ODEBUG_POOL_MIN_LEVEL;
>>
>> As debug_objects_pool_min_level is the minimum level to keep around and
>> obj_pool_min_free is a statistics mechanism, __data_racy is misplaced
>> too. The variables should swap their position, because
>> debug_objects_pool_min_level is functional, but obj_pool_min_free is
>> pure stats.

This principle covers a large number of variables. It should be sorted
by the variable name before. It's better not to change the position this time.

>>
>> Also debug_objects_pool_min_level and debug_objects_pool_size should
>> be __ro_after_init.
> 
> OK, How about modifying it like this? I further removed the __data_racy from
> debug_objects_pool_min_level and debug_objects_pool_size, because __ro_after_init.
> 
> 
> diff --git a/lib/debugobjects.c b/lib/debugobjects.c
> index d3845705db955fa..816d3d968cd9f14 100644
> --- a/lib/debugobjects.c
> +++ b/lib/debugobjects.c
> @@ -70,7 +70,8 @@ static HLIST_HEAD(obj_to_free);
>   * made at debug_stats_show(). Both obj_pool_min_free and obj_pool_max_used
>   * can be off.
>   */
> -static int                     obj_pool_min_free = ODEBUG_POOL_SIZE;
> +static int __ro_after_init     debug_objects_pool_size = ODEBUG_POOL_SIZE;
> +static int __ro_after_init     debug_objects_pool_min_level = ODEBUG_POOL_MIN_LEVEL;
>  static int                     obj_pool_free = ODEBUG_POOL_SIZE;
>  static int                     obj_pool_used;
>  static int                     obj_pool_max_used;
> @@ -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;
> 
>  static const struct debug_obj_descr *descr_test  __read_mostly;
>  static struct kmem_cache       *obj_cache __ro_after_init;
> 
> 
>>
>>> Fixes: d26bf5056fc0 ("debugobjects: Reduce number of pool_lock acquisitions in fill_pool()")
>>> Fixes: 36c4ead6f6df ("debugobjects: Add global free list and the counter")
>>
>> Nice detective work!
>>
>> Thanks,
>>
>>         tglx
>> .
>>
> 

-- 
Regards,
  Zhen Lei