From: Chanwoo Choi <cw00.choi@samsung.com>
To: Leonard Crestez <leonard.crestez@nxp.com>,
Matthias Kaehlcke <mka@chromium.org>,
MyungJoo Ham <myungjoo.ham@samsung.com>,
Kyungmin Park <kyungmin.park@samsung.com>
Cc: "Artur Świgoń" <a.swigon@partner.samsung.com>,
"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"Krzysztof Kozlowski" <krzk@kernel.org>,
"Lukasz Luba" <l.luba@partner.samsung.com>
Subject: Re: [PATCH] PM / devfreq: Check NULL governor in available_governors_show
Date: Tue, 24 Sep 2019 16:25:05 +0900 [thread overview]
Message-ID: <cf1d1470-e62c-84e4-a926-156baf8aed18@samsung.com> (raw)
In-Reply-To: <VI1PR04MB70231013FC39AA9A4AD46AC0EE840@VI1PR04MB7023.eurprd04.prod.outlook.com>
On 19. 9. 24. 오후 4:17, Leonard Crestez wrote:
> On 2019-09-24 4:48 AM, Chanwoo Choi wrote:
>> On 19. 9. 24. 오전 1:34, Leonard Crestez wrote:
>>> The governor is initialized after sysfs attributes become visible so in
>>> theory the governor field can be NULL here.
>>>
>>> Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
>>> ---
>>> drivers/devfreq/devfreq.c | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> Found this by hacking device core to call attribute "show" functions
>>> from inside device_add.
>>>
>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>> index 00fc23fea5b2..896fb2312f2f 100644
>>> --- a/drivers/devfreq/devfreq.c
>>> +++ b/drivers/devfreq/devfreq.c
>>> @@ -1322,11 +1322,11 @@ static ssize_t available_governors_show(struct device *d,
>>>
>>> /*
>>> * The devfreq with immutable governor (e.g., passive) shows
>>> * only own governor.
>>> */
>>> - if (df->governor->immutable) {
>>> + if (df->governor && df->governor->immutable) {
>>> count = scnprintf(&buf[count], DEVFREQ_NAME_LEN,
>>> "%s ", df->governor_name);
>>> /*
>>> * The devfreq device shows the registered governor except for
>>> * immutable governors such as passive governor .
>>>
>>
>> As you mentioned, it create sysfs and then initialize the governor instance
>> as following:
>>
>> device_register()
>> device_add()
>> device_add_attrs()
>> creating sysfs entries.
>> governor = try_then_request_governor(...)
>>
>>
>> Thanks for fix-up.
>> Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
>>
>> Additionally, you have to add the following 'fixes' tag
>> and then send it to stable mailing list(stable@vger.kernel.org).
>> - Fixes: bcf23c79c4e46 ("PM / devfreq: Fix available_governor sysfs")
>
> OK, but I'm not sure this meets the criteria for inclusion into linux
> stable:
>
> * It must fix a real bug that bothers people (not a, "This could be a
> problem..." type thing).
> * No "theoretical race condition" issues, unless an explanation of how
> the race can be exploited is also provided.
OK. If you think that it is not necessary to send it to stable mailing list,
don't send it. Thanks.
>
> This patch fixes a theoretical race condition which has been there since
> the start.
>
> --
> Regards,
> Leonard
>
--
Best Regards,
Chanwoo Choi
Samsung Electronics
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prev parent reply other threads:[~2019-09-24 7:21 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20190923163453epcas4p1f9cff7d9f1a33fabcf4c980560d6c27d@epcas4p1.samsung.com>
2019-09-23 16:34 ` [PATCH] PM / devfreq: Check NULL governor in available_governors_show Leonard Crestez
2019-09-23 18:50 ` Matthias Kaehlcke
2019-09-24 1:52 ` Chanwoo Choi
2019-09-24 7:17 ` Leonard Crestez
2019-09-24 7:25 ` Chanwoo Choi [this message]
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