linux-kernel - Re: [PATCH] soc: qcom: icc-bwmon: Fix handling dev_pm_opp_find_bw

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Message-ID: <ddadd8cb-9738-4540-8c37-98e3aa93012f@linaro.org>
Date: Sat, 16 Aug 2025 10:40:33 +0200
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
 Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>,
 Thara Gopinath <thara.gopinath@...il.com>, linux-arm-msm@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: stable@...r.kernel.org, Dan Carpenter <dan.carpenter@...aro.org>
Subject: Re: [PATCH] soc: qcom: icc-bwmon: Fix handling dev_pm_opp_find_bw_*()
 errors

On 14/08/2025 13:27, Konrad Dybcio wrote:
> On 8/14/25 1:25 PM, Krzysztof Kozlowski wrote:
>> On 14/08/2025 11:15, Konrad Dybcio wrote:
>>> On 8/14/25 8:32 AM, Krzysztof Kozlowski wrote:
>>>> The ISR calls dev_pm_opp_find_bw_ceil(), which can return EINVAL, ERANGE
>>>> or ENODEV, and if that one fails with ERANGE, then it tries again with
>>>> floor dev_pm_opp_find_bw_floor().
>>>>
>>>> Code misses error checks for two cases:
>>>> 1. First dev_pm_opp_find_bw_ceil() failed with error different than
>>>>    ERANGE,
>>>> 2. Any error from second dev_pm_opp_find_bw_floor().
>>>>
>>>> In an unlikely case these error happened, the code would further
>>>> dereference the ERR pointer.  Close that possibility and make the code
>>>> more obvious that all errors are correctly handled.
>>>>
>>>> Reported by Smatch:
>>>>   icc-bwmon.c:693 bwmon_intr_thread() error: 'target_opp' dereferencing possible ERR_PTR()
>>>>
>>>> Fixes: b9c2ae6cac40 ("soc: qcom: icc-bwmon: Add bandwidth monitoring driver")
>>>> Cc: <stable@...r.kernel.org>
>>>> Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
>>>> Closes: https://lore.kernel.org/r/aJTNEQsRFjrFknG9@stanley.mountain/
>>>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>>>>
>>>> ---
>>>>
>>>> Some unreleased smatch, though, because I cannot reproduce the warning,
>>>> but I imagine Dan keeps the tastiests reports for later. :)
>>>> ---
>>>>  drivers/soc/qcom/icc-bwmon.c | 3 +++
>>>>  1 file changed, 3 insertions(+)
>>>>
>>>> diff --git a/drivers/soc/qcom/icc-bwmon.c b/drivers/soc/qcom/icc-bwmon.c
>>>> index 3dfa448bf8cf..597f9025e422 100644
>>>> --- a/drivers/soc/qcom/icc-bwmon.c
>>>> +++ b/drivers/soc/qcom/icc-bwmon.c
>>>> @@ -656,6 +656,9 @@ static irqreturn_t bwmon_intr_thread(int irq, void *dev_id)
>>>>  	if (IS_ERR(target_opp) && PTR_ERR(target_opp) == -ERANGE)
>>>>  		target_opp = dev_pm_opp_find_bw_floor(bwmon->dev, &bw_kbps, 0);
>>>>  
>>>> +	if (IS_ERR(target_opp))
>>>> +		return IRQ_HANDLED;
>>>
>>> So the thunk above checks for a ceil freq relative to bw_kbps and then
>>> if it doesn't exist, for a floor one
>>>
>>> Meaning essentially if we fall into this branch, there's no OPPs in the
>>> table, which would have been caught in probe
>> Yes, unless:
>> 1. There is a bug in the opp code
>> 2. Probe code is anyhow changed in the future
>>
>> I think the code should be readable and obviouswithin the function, not
>> depend on some pre-checks in the probe. But if you think that's
>> defensive coding I can also add a comment to silence future Smatch
>> complains.
> 
> I ultimately don't *really* mind either, just wanted to point out that
> currently it's effectively a false positive
I will adjust the commit msg to point out that it is actually impossible
condition now.

Best regards,
Krzysztof