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

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Message-ID: <f2400037-c39c-4266-9e77-b084bd5f9395@linaro.org>
Date: Thu, 14 Aug 2025 13:25:23 +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 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.

Best regards,
Krzysztof