linux-kernel - Re: [PATCH] coresight: etm4x: Ensure valid drvdata and clock before clk

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Message-ID: <435813e1-3e26-d125-d706-a2e3d8fd4e45@arm.com>
Date:   Wed, 16 Aug 2023 13:36:29 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     James Clark <james.clark@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     Mike Leach <mike.leach@...aro.org>, coresight@...ts.linaro.org,
        linux-kernel@...r.kernel.org,
        Dan Carpenter <dan.carpenter@...aro.org>
Subject: Re: [PATCH] coresight: etm4x: Ensure valid drvdata and clock before
 clk_put()



On 8/11/23 15:44, James Clark wrote:
> 
> 
> On 11/08/2023 10:22, Anshuman Khandual wrote:
>>
>>
>> On 8/11/23 14:39, Suzuki K Poulose wrote:
>>> On 11/08/2023 09:39, James Clark wrote:
>>>>
>>>>
>>>> On 11/08/2023 07:27, Anshuman Khandual wrote:
>>>>> This validates 'drvdata' and 'drvdata->pclk' clock before calling clk_put()
>>>>> in etm4_remove_platform_dev(). The problem was detected using Smatch static
>>>>> checker as reported.
>>>>>
>>>>> Cc: Suzuki K Poulose <suzuki.poulose@....com>
>>>>> Cc: Mike Leach <mike.leach@...aro.org>
>>>>> Cc: James Clark <james.clark@....com>
>>>>> Cc: coresight@...ts.linaro.org
>>>>> Cc: linux-arm-kernel@...ts.infradead.org
>>>>> Cc: linux-kernel@...r.kernel.org
>>>>> Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
>>>>> Closes: https://lists.linaro.org/archives/list/coresight@lists.linaro.org/thread/G4N6P4OXELPLLQSNU3GU2MR4LOLRXRMJ/
>>>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
>>>>> ---
>>>>> This applies on coresight-next
>>>>>
>>>>>   drivers/hwtracing/coresight/coresight-etm4x-core.c | 2 +-
>>>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>>>> index 703b6fcbb6a5..eb412ce302cc 100644
>>>>> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>>>> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>>>> @@ -2269,7 +2269,7 @@ static int __exit etm4_remove_platform_dev(struct platform_device *pdev)
>>>>>           etm4_remove_dev(drvdata);
>>>>>       pm_runtime_disable(&pdev->dev);
>>>>>   -    if (drvdata->pclk)
>>>>> +    if (drvdata && drvdata->pclk && !IS_ERR(drvdata->pclk))
>>>>>           clk_put(drvdata->pclk);
>>>>>         return 0;
>>>>
>>>> It could be !IS_ERR_OR_NULL(drvdata->pclk), but I wouldn't bother
>>>> changing it at this point.
>>>
>>> +1, please could we have that. Someone else will run a code scanner and
>>> send a patch later. Given this is straight and easy change, lets do it
>>> in the first place.
>>
>> But we already have a drvdata->pclk validation check before IS_ERR().
>> Would not _OR_NULL be redundant ?
> 
> I meant that it could be replaced with the single check:
> 
>   if (drvdata && !IS_ERR_OR_NULL(drvdata->pclk))
>       clk_put(drvdata->pclk);
> 
> As Dan mentions it can't be an error pointer anyway, but leaving it like
> this could just be considered defensive coding.

Let's just go with the above change as you had suggested unless there is any
particular objection.

if (drvdata && !IS_ERR_OR_NULL(drvdata->pclk))
	clk_put(drvdata->pclk);