linux-kernel - Re: [PATCH v1 3/7] powercap/dtpm: Fixup kfree for virtual node

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Message-ID: <e44b9c4b-2ac4-4ea4-c771-bde13943af5f@linaro.org>
Date:   Wed, 16 Feb 2022 19:10:33 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     rjw@...ysocki.net, heiko@...ech.de, lukasz.luba@....com,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Daniel Lezcano <daniel.lezcano@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH v1 3/7] powercap/dtpm: Fixup kfree for virtual node

On 16/02/2022 17:22, Ulf Hansson wrote:
> On Sun, 30 Jan 2022 at 22:02, Daniel Lezcano <daniel.lezcano@...aro.org> wrote:
>>
>> When the node is virtual there is no release function associated which
>> can free the memory.
>>
>> Free the memory when no 'ops' exists.
>>
>> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
>> ---
>>   drivers/powercap/dtpm.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/powercap/dtpm.c b/drivers/powercap/dtpm.c
>> index 0b0121c37a1b..7bddd25a6767 100644
>> --- a/drivers/powercap/dtpm.c
>> +++ b/drivers/powercap/dtpm.c
>> @@ -181,12 +181,12 @@ int dtpm_release_zone(struct powercap_zone *pcz)
>>
>>          if (dtpm->ops)
>>                  dtpm->ops->release(dtpm);
>> +       else
>> +               kfree(dtpm);
>>
> 
> This doesn't look correct. Below you check dtpm against "root", which
> may be after its memory has been freed.
> 
> If the ->release() function should be responsible for freeing the
> dtpm, it needs to be called after the check below.

It is harmless, 'root' is not dereferenced but used as an ID

Moreover, in the patch 5/7 it is moved out this function.


>>          if (root == dtpm)
>>                  root = NULL;
>>
>> -       kfree(dtpm);
>> -
>>          return 0;
>>   }
>>
> 
> Kind regards
> Uffe


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