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Subject: Re: [RFC PATCH v7 6/9] media: tegra: Add Tegra210 Video input driver
From:   Sowjanya Komatineni <skomatineni@nvidia.com>
To:     Dmitry Osipenko <digetx@gmail.com>
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Sorry please ignore.

We can't free vi during v4l2 device release as when no device nodes are=20
opened, vi free happens right away during host1x_video_remove.

With this tegra-video driver unbind ->bind will not work as vi memory=20
allocated during vi_probe gets freed during v4l2 device release so=20
during bind init() callback execution will crash as vi got freed while=20
vi driver is still bound to device.

Will wait for Hans/Thierry comments as I see dependency depending on=20
where unbind/bind happens.


On 4/15/20 4:08 PM, Sowjanya Komatineni wrote:
> With minor change of not using vi reference after=20
> host1x_client_unregister and freeing vi during v4l2 device release works.
>
> For csi, we can use devm_kzalloc for now untill we decide later if we=20
> want to expose async subdev nodes during sensor support.
>
> Will have this fix in v8 with a comment in vi_remove to make sure not=20
> to use vi reference after host1x_client_unregister.
>
> Will test more and will release v8 with above fix to allow direct=20
> host1x client driver unbind.
>
> Thanks
>
> sowjanya
>
>
> On 4/15/20 12:51 PM, Sowjanya Komatineni wrote:
>>
>> On 4/15/20 12:21 PM, Dmitry Osipenko wrote:
>>> External email: Use caution opening links or attachments
>>>
>>>
>>> 15.04.2020 21:53, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
>>> ...
>>>>>>>>>> Have you tried to test this driver under KASAN? I suspect that
>>>>>>>>>> you just
>>>>>>>>>> masked the problem, instead of fixing it.
>>>> Tested with kmemleak scan and did not see any memory leaks
>>> You should get use-after-free and not memleak.
>> I don't see use-after-free bugs during the testing.
>>
>> But as mentioned when direct vi/csi client driver unbind happens=20
>> while video device node is kept opened, vi driver remove will free vi=20
>> structure memory but actual video device memory which is part of=20
>> channels remains but list head gets lost when vi structure is freed.
>>
>> So, when device node is released and executes release callback as=20
>> list head is lost it can't free allocated channels which is not good.
>>
>> This happens only with direct host1x client vi/csi driver unbind.
>>
>> Need to find better place to free host1x client driver data structure=20
>> to allow direct client driver unbind->bind.
>>