linux-kernel - Re: [PATCH 1/3] phy: qcom-qmp-usb: fix NULL pointer dereference in PM callbacks

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Message-ID: <8753d857-5d72-493b-8c39-8caa84e0ba16@oss.qualcomm.com>
Date: Tue, 26 Aug 2025 14:09:58 +0530
From: Kathiravan Thirumoorthy <kathiravan.thirumoorthy@....qualcomm.com>
To: Bjorn Andersson <andersson@...nel.org>
Cc: Vinod Koul <vkoul@...nel.org>, Kishon Vijay Abraham I
 <kishon@...nel.org>,
        Dmitry Baryshkov <lumag@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, linux-arm-msm@...r.kernel.org,
        linux-phy@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Poovendhan Selvaraj <quic_poovendh@...cinc.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH 1/3] phy: qcom-qmp-usb: fix NULL pointer dereference in PM
 callbacks


On 8/26/2025 8:20 AM, Bjorn Andersson wrote:
> On Mon, Aug 25, 2025 at 05:22:02PM +0530, Kathiravan Thirumoorthy wrote:
>> From: Poovendhan Selvaraj <quic_poovendh@...cinc.com>
>>
>> The pm ops are enabled before qmp phy create which causes
>> a NULL pointer dereference when accessing qmp->phy->init_count
>> in the qmp_usb_runtime_suspend.
>>
> How does that happen? Do we end up in the error path inbetween the
> devm_pm_runtime_enable()? Or does it happen by some other means?


qmp_usb_probe() is scheduled out per the below stack (collected from the 
RAM dump),


Stack trace of the kmodloader process:
     [<0x408def88>] __schedule+0x348/0x55c
     [<0x408df1f8>] schedule+0x5c/0x98
     [<0x4052c318>] rpm_resume+0x150/0x404
     [<0x4052d4e4>] pm_runtime_forbid+0x54/0x60
     [<0x629c47f0>] qmp_usb_probe+0x3c4/0x5d0 [phy_qcom_qmp_usb.ko]

 From the above snippet, we can see that the phy-create has not happened 
yet as the probe is still in pm_runtime_forbid() and qmp->phy is NULL. 
Meanwhile, qmp_usb_runtime_suspend() is called, causing the NULL pointer 
de-reference issue. Since the issue is not easily reproducible, we are 
not able to find out who/why the suspend was called.


>
> This would be quite useful information for others to know if they hit
> the same or just a similar problem.
>
>> So if qmp->phy is NULL, bail out early in suspend / resume callbacks
>> to avoid the NULL pointer dereference in qmp_usb_runtime_suspend and
>> qmp_usb_runtime_resume.
>>
>> Below is the stacktrace for reference:
>>
>> [<818381a0>] (qmp_usb_runtime_suspend [phy_qcom_qmp_usb]) from [<4051d1d8>] (__rpm_callback+0x3c/0x110)
>> [<4051d1d8>] (__rpm_callback) from [<4051d2fc>] (rpm_callback+0x50/0x54)
>> [<4051d2fc>] (rpm_callback) from [<4051d940>] (rpm_suspend+0x23c/0x428)
>> [<4051d940>] (rpm_suspend) from [<4051e808>] (pm_runtime_work+0x74/0x8c)
>> [<4051e808>] (pm_runtime_work) from [<401311f4>] (process_scheduled_works+0x1d0/0x2c8)
>> [<401311f4>] (process_scheduled_works) from [<40131d48>] (worker_thread+0x260/0x2e4)
>> [<40131d48>] (worker_thread) from [<40138970>] (kthread+0x118/0x12c)
>> [<40138970>] (kthread) from [<4010013c>] (ret_from_fork+0x14/0x38)
>>
>> Cc: stable@...r.kernel.org # v6.0
>> Fixes: 65753f38f530 ("phy: qcom-qmp-usb: drop multi-PHY support")
> Has this been a reproducible issue for last 3 years? I think the fixes
> makes sense in that it introduced the indirection, but when did the
> issue actually show up?


After migrating the QSDK Linux from 5.4 to 6.6, we are started seeing 
this issue randomly. We didn't had a chance to test in the other kernel 
versions.


>
> Regards,
> Bjorn
>
>> Signed-off-by: Poovendhan Selvaraj <quic_poovendh@...cinc.com>
>> Signed-off-by: Kathiravan Thirumoorthy <kathiravan.thirumoorthy@....qualcomm.com>
>> ---
>>   drivers/phy/qualcomm/phy-qcom-qmp-usb.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/phy/qualcomm/phy-qcom-qmp-usb.c b/drivers/phy/qualcomm/phy-qcom-qmp-usb.c
>> index ed646a7e705ba3259708775ed5fedbbbada13735..cd04e8f22a0fe81b086b308d02713222aa95cae3 100644
>> --- a/drivers/phy/qualcomm/phy-qcom-qmp-usb.c
>> +++ b/drivers/phy/qualcomm/phy-qcom-qmp-usb.c
>> @@ -1940,7 +1940,7 @@ static int __maybe_unused qmp_usb_runtime_suspend(struct device *dev)
>>   
>>   	dev_vdbg(dev, "Suspending QMP phy, mode:%d\n", qmp->mode);
>>   
>> -	if (!qmp->phy->init_count) {
>> +	if (!qmp->phy || !qmp->phy->init_count) {
>>   		dev_vdbg(dev, "PHY not initialized, bailing out\n");
>>   		return 0;
>>   	}
>> @@ -1960,7 +1960,7 @@ static int __maybe_unused qmp_usb_runtime_resume(struct device *dev)
>>   
>>   	dev_vdbg(dev, "Resuming QMP phy, mode:%d\n", qmp->mode);
>>   
>> -	if (!qmp->phy->init_count) {
>> +	if (!qmp->phy || !qmp->phy->init_count) {
>>   		dev_vdbg(dev, "PHY not initialized, bailing out\n");
>>   		return 0;
>>   	}
>>
>> -- 
>> 2.34.1
>>