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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>, <thierry.reding@gmail.com>,
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On 4/15/20 10:21 AM, Sowjanya Komatineni wrote:
>
> On 4/15/20 9:54 AM, Sowjanya Komatineni wrote:
>>
>> On 4/15/20 7:22 AM, Dmitry Osipenko wrote:
>>> External email: Use caution opening links or attachments
>>>
>>>
>>> 15.04.2020 05:57, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
>>>> +static int tegra_csi_remove(struct platform_device *pdev)
>>>> +{
>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 struct tegra_csi *csi =3D platform_get_drvda=
ta(pdev);
>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 int err;
>>>> +
>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 err =3D host1x_client_unregister(&csi->clien=
t);
>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 if (err < 0) {
>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0 dev_err(csi->dev,
>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 "failed to unregister h=
ost1x client: %d\n",=20
>>>> err);
>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0 return err;
>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 }
>>>> +
>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 pm_runtime_disable(csi->dev);
>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 kfree(csi);
>>> IIRC, the driver removal is invoked on the unbinding. Hence, I'm not
>>> sure how moving away from the resource-managed API helps here. Could=20
>>> you
>>> please explain in a more details?
>>>
>>> Have you tried to test this driver under KASAN? I suspect that you just
>>> masked the problem, instead of fixing it.
>> Using devm_kzalloc for vi/csi structures based on prior feedback=20
>> request to switch to use kzalloc all over this driver.
>>
>> Hi Hans,
>>
>> video devices lifetime is till video device nodes are released. So,=20
>> v4l2 device release callback does the release of tegra channel=20
>> allocation which hold video device.
>>
>> Below are the 3 possible cases of unbind/unload,
>>
>> 1. during tegra-video module unload, if v4l2 device refcnt is not 0=20
>> which is the case when any of video device node handle is kept opened=20
>> then unloading module will not happen and module refcnt is also=20
>> non-zero and unloading tegra-video module reports module in use.
>>
>> 2. during tegra-video driver unbind, tegra-video driver removal will=20
>> do vi/csi clients exit ops which unregisters video device allocated=20
>> memory during release callback of v4l2 device. vi/csi structure=20
>> allocation remains same as vi/csi driver removal will not happen in=20
>> this case.
>>
>>
>> 3. during direct host1x client drivers vi/csi unbind, both=20
>> host1x_clients vi/csi gets unregistered, deletes host1x logical=20
>> device which executes tegra-video driver removal() -> vi/csi exit()=20
>> before vi/csi memory gets freed in vi/csi driver remove().
>>
>> So, any active streaming will stop and video devices are unregistered=20
>> during direct client driver unbind prior to freeing vi/csi memory.
>>
>> Also vi/csi driver remove does explicit free vi/csi as its allocated=20
>> with kzalloc. So not sure how using kzalloc is different to=20
>> devm_kzalloc for vi/csi structure in terms of when vi/csi memory gets=20
>> freed?
>>
>> Except for channel allocation which holds video device and as video=20
>> device life time is beyond tegra-video module unbind->vi exit(),=20
>> looks like we can use devm_kzalloc for vi/csi.
>>
>>
>> Can you please comment if you still think we need to use kzalloc=20
>> rather than devm_kzalloc for vi/csi structure allocation?
>>
>> Thanks
>>
>> Sowjanya
>>
> One more case is when video device node is kept opened with v4l2-ctl=20
> sleep (rather than streaming), where it will keep device node open for=20
> specified time and if direct vi client driver unbind happens then vi=20
> driver remove() will free vi memory before v4l2 device release happens.
>
> But I don't see any crash or errors with this case.
>
> Also if we allow direct client driver unbind, then vi structure memory=20
> lifetime should also be till v4l2 device release happens.
>
> But we can free vi in v4l2 device release callback as in case when=20
> device node is not kept opened, video device release happens immediate=20
> and we cant free vi that early.

typo fix:

But we can't free vi structure memory allocation in v4l2 device release=20
callback as in case when device node is not kept opened, device release=20
happens immediate and we can't free vi structure memory that early.

>
> Hans/Thierry, Can you please comment on this case?
>
> Thanks
>
> Sowjanya
>