linux-kernel - Re: [PATCH] percpu_counter: Remove debug_object

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Message-ID: <5703acbf-da53-7409-7d73-f48e580ce1cd@codeaurora.org>
Date:   Mon, 27 Aug 2018 12:26:32 +0530
From:   "Kohli, Gaurav" <gkohli@...eaurora.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     gregkh@...uxfoundation.org, nborisov@...e.com,
        akpm@...ux-foundation.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] percpu_counter: Remove debug_object_free call twice

Hi ,

Sorry for very late reminder, just wanted to know is below understanding 
of code is wrong?

Regards
Gaurav

On 4/17/2018 11:59 AM, Kohli, Gaurav wrote:
> On 4/17/2018 3:18 AM, Tejun Heo wrote:
> 
>> On Fri, Apr 13, 2018 at 03:05:03PM +0530, Gaurav Kohli wrote:
>>> During percpu_counter destroy, debug_object_free is calling
>>> twice which may create race. So removing once instance of call
>>> from debug_percpu_counter_deactivate.
>> I don't quite follow.  Can you please elaborate how it can be called
>> twice?
> 
> Hi Tejun,
> 
> In percpu_counter_fixup_free function, first call is 
> percpu_counter_destroy -> debug_percpu_counter_deactivate (this will set 
> inactive and free the debug object as well for percpu counter) -> 
> free_percpu (finally freeing the counters).
> 
> Below is the code snippet:
> 
>          case DEBUG_STATE_ACTIVE:
> 
>                  percpu_counter_destroy(fbc); -> first call
> 
>                  debug_object_free(fbc, &percpu_counter_debug_descr); -> 
> this will again call the same debug object free, if somehow counters 
> will reinitialize between these two calls.
> 
> 
> We are seeing one race condition issue where one object of db list is 
> corrupted and just before object of that corrupted node is 
> percpu_counter, Still i am not sure the reason of race as it is very
> 
> difficult to reproduce. But i have found this during code review. Please 
> correct me, if i misunderstood this.
> 
>>
>> Thanks.
>>
>>

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