linux-kernel - Re: [PATCH v4 0/7] OPP: Add support to find OPP for a set of keys

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Message-ID: <20250826053606.zktmwgfdwymizv6k@vireshk-i7>
Date: Tue, 26 Aug 2025 11:06:06 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Wasim Nazir <wasim.nazir@....qualcomm.com>
Cc: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>,
	Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
	Stephen Boyd <sboyd@...nel.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Manivannan Sadhasivam <mani@...nel.org>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kwilczynski@...nel.org>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v4 0/7] OPP: Add support to find OPP for a set of keys

On 26-08-25, 10:50, Viresh Kumar wrote:
> On 25-08-25, 22:14, Wasim Nazir wrote:
> > Kernel log:
> > Unable to handle kernel NULL pointer dereference at virtual address 0000000000000016
> > ...
> > Call trace:
> >  _read_bw+0x0/0x10 (P)
> >  _find_key+0xb8/0x194
> >  dev_pm_opp_find_bw_floor+0x54/0x8c
> >  bwmon_intr_thread+0x84/0x284 [icc_bwmon]
> >  irq_thread_fn+0x2c/0xa8
> >  irq_thread+0x174/0x334
> >  kthread+0x134/0x208
> >  ret_from_fork+0x10/0x20
> 
> Hmm, this happened because it is possible for the `opp` to be invalid
> (error) even if `_compare_floor()` returned true, if the target key is
> lower than the lowest freq of the table.
> 
> Dropped the patch for now anyway.

Can you help me testing this over your failing branch please ?

diff --git a/drivers/opp/core.c b/drivers/opp/core.c
index 81fb7dd7f323..5b24255733b5 100644
--- a/drivers/opp/core.c
+++ b/drivers/opp/core.c
@@ -554,10 +554,10 @@ static struct dev_pm_opp *_opp_table_find_key(struct opp_table *opp_table,
        list_for_each_entry(temp_opp, &opp_table->opp_list, node) {
                if (temp_opp->available == available) {
                        if (compare(&opp, temp_opp, read(temp_opp, index), *key)) {
-                               *key = read(opp, index);
-
-                               /* Increment the reference count of OPP */
-                               dev_pm_opp_get(opp);
+                               if (!IS_ERR(opp)) {
+                                       *key = read(opp, index);
+                                       dev_pm_opp_get(opp);
+                               }
                                break;
                        }
                }

-- 
viresh