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

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Message-ID: <aJ85PQbujQe-IZUH@stanley.mountain>
Date: Fri, 15 Aug 2025 16:42:21 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: 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,
	stable@...r.kernel.org
Subject: Re: [PATCH] soc: qcom: icc-bwmon: Fix handling
 dev_pm_opp_find_bw_*() errors

On Thu, Aug 14, 2025 at 11:15:08AM +0200, 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

It would be really hard to silence a false positive like this...

regards,
dan carpenter