netdev - Re: [PATCH v3 net-next 01/23] lib: add reference counting tracking infrastructure

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Date:   Wed, 8 Dec 2021 16:11:03 +0100
From:   Andrzej Hajda <andrzej.hajda@...el.com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>, Greg KH <greg@...ah.com>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v3 net-next 01/23] lib: add reference counting tracking
 infrastructure


On 08.12.2021 15:59, Jakub Kicinski wrote:
> On Wed, 8 Dec 2021 15:09:17 +0100 Andrzej Hajda wrote:
>> On 05.12.2021 05:21, Eric Dumazet wrote:
>>> From: Eric Dumazet <edumazet@...gle.com>
>>>
>>> It can be hard to track where references are taken and released.
>>>
>>> In networking, we have annoying issues at device or netns dismantles,
>>> and we had various proposals to ease root causing them.
>>>
>>> This patch adds new infrastructure pairing refcount increases
>>> and decreases. This will self document code, because programmers
>>> will have to associate increments/decrements.
>>>
>>> This is controled by CONFIG_REF_TRACKER which can be selected
>>> by users of this feature.
>>>
>>> This adds both cpu and memory costs, and thus should probably be
>>> used with care.
>>>
>>> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
>>> Reviewed-by: Dmitry Vyukov <dvyukov@...gle.com>
>> Life is surprising, I was working on my own framework, solving the same
>> issue, with intention to publish it in few days :)
>>
>> My approach was little different:
>>
>> 1. Instead of creating separate framework I have extended debug_objects.
>>
>> 2. There were no additional fields in refcounted object and trackers -
>> infrastructure of debug_objects was reused - debug_objects tracked both
>> pointers of refcounted object and its users.
>>
>>
>> Have you considered using debug_object? it seems to be good place to put
>> it there, I am not sure about performance differences.
> Something along these lines?
>
> https://lore.kernel.org/all/20211117174723.2305681-1-kuba@kernel.org/
>
> ;)


Ups, I was not clear in my last sentence, I meant "extend debug_objects 
with tracking users of the object" :)


Regards

Andrzej


>
>> One more thing about design - as I understand CONFIG_REF_TRACKER turns
>> on all trackers in whole kernel, have you considered possibility/helpers
>> to enable/disable tracking per class of objects?