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

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Message-ID: <e35ca54c-252f-45c4-bfdf-fd943f833bc4@oss.qualcomm.com>
Date: Thu, 14 Aug 2025 11:15:08 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        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 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

Konrad