linux-kernel - Re: [PATCH v2] media: qcom: camss: fix VFE pm domain off

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Message-ID: <5cccec71-0cc7-492a-9fb9-903970da05c5@linaro.org>
Date: Fri, 29 Nov 2024 11:06:02 +0000
From: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To: Vladimir Zapolskiy <vladimir.zapolskiy@...aro.org>,
 Barnabás Czémán <barnabas.czeman@...nlining.org>,
 Robert Foss <rfoss@...nel.org>, Todor Tomov <todor.too@...il.com>,
 Mauro Carvalho Chehab <mchehab@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>, Hans Verkuil <hverkuil@...all.nl>
Cc: linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
 linux-kernel@...r.kernel.org, Yassine Oudjana <y.oudjana@...tonmail.com>
Subject: Re: [PATCH v2] media: qcom: camss: fix VFE pm domain off

On 29/11/2024 08:48, Vladimir Zapolskiy wrote:
> On 11/28/24 21:39, Barnabás Czémán wrote:
>> Fix NULL pointer check before device_link_del
>> is called.
>>
>> Unable to handle kernel NULL pointer dereference at virtual address 
>> 000000000000032c
>> Call trace:
>>   device_link_put_kref+0xc/0xb8
>>   device_link_del+0x30/0x48
>>   vfe_pm_domain_off+0x24/0x38 [qcom_camss]
>>   vfe_put+0x9c/0xd0 [qcom_camss]
>>   vfe_set_power+0x48/0x58 [qcom_camss]
>>   pipeline_pm_power_one+0x154/0x158 [videodev]
>>   pipeline_pm_power+0x74/0xfc [videodev]
>>   v4l2_pipeline_pm_use+0x54/0x90 [videodev]
>>   v4l2_pipeline_pm_put+0x14/0x34 [videodev]
>>   video_release+0x2c/0x44 [qcom_camss]
>>   v4l2_release+0xe4/0xec [videodev]
>>
>> Fixes: eb73facec2c2 ("media: qcom: camss: Use common VFE pm_domain_on/ 
>> pm_domain_off where applicable")
>> Tested-by: Yassine Oudjana <y.oudjana@...tonmail.com>
>> Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
>> Signed-off-by: Barnabás Czémán <barnabas.czeman@...nlining.org>
>> ---
>> Changes in v2:
>> - Add backtrace to the commit message.
>> - Link to v1: https://lore.kernel.org/r/20241122-vfe_pm_domain_off- 
>> v1-1-81d18f56563d@...nlining.org
>> ---
>>   drivers/media/platform/qcom/camss/camss-vfe.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/media/platform/qcom/camss/camss-vfe.c b/drivers/ 
>> media/platform/qcom/camss/camss-vfe.c
>> index 
>> 80a62ba11295042802cbaec617fb87c492ea6a55..1bf1473331f63b9ab106d21ea263c84d851c8a31 100644
>> --- a/drivers/media/platform/qcom/camss/camss-vfe.c
>> +++ b/drivers/media/platform/qcom/camss/camss-vfe.c
>> @@ -595,7 +595,7 @@ void vfe_isr_reset_ack(struct vfe_device *vfe)
>>    */
>>   void vfe_pm_domain_off(struct vfe_device *vfe)
>>   {
>> -    if (!vfe->genpd)
>> +    if (!vfe->genpd_link)
>>           return;
>>       device_link_del(vfe->genpd_link);
>>
> 
> I object to this change, there might be a problem in the code, however it
> is not yet identified.
> 
> vfe->genpd is not NULL, if vfe_pm_domain_on()/vfe_pm_domain_off() are
> called appropriately, the "fix" does not fix the real problem, it veils it.
> 
> -- 
> Best wishes,
> Vladimir
> 
> 

Let's walk through the logic.

vfe->genpd =

Can happen in vfe_subdev_init();

vfe_pm_domain_on() can fail @ vfe->genpd_link =

If it fails then I _suppose_ we are still calling vfe_pm_domain_off() at 
least that's the only logically way I see this error can manifest.

@Barnabás can you confirm that this is the case ?

If not, can you please provide more detail ?

---
bod