Re: [RFC PATCH v3 4/6] media: tegra: Add Tegra210 Video input driver

[Sowjanya Komatineni <skomatineni@nvidia.com>]

On 3/18/20 4:48 AM, Hans Verkuil wrote:
> External email: Use caution opening links or attachments
>
>
> On 2/24/20 5:45 AM, Sowjanya Komatineni wrote:
>> On 2/20/20 11:11 AM, Sowjanya Komatineni wrote:
>>> On 2/20/20 5:33 AM, Hans Verkuil wrote:
>>>> External email: Use caution opening links or attachments
>>>>
>>>>
>>>> (Replying to myself so I can explain this a bit more)
>>>>
>>>> On 2/20/20 1:44 PM, Hans Verkuil wrote:
>>>>>> +
>>>>>> +static int tegra_csi_tpg_channels_alloc(struct tegra_csi *csi)
>>>>>> +{
>>>>>> +    struct device_node *node = csi->dev->of_node;
>>>>>> +    unsigned int port_num;
>>>>>> +    int ret;
>>>>>> +    struct tegra_csi_channel *item;
>>>>>> +    unsigned int tpg_channels = csi->soc->csi_max_channels;
>>>>>> +
>>>>>> +    /* allocate CSI channel for each CSI x2 ports */
>>>>>> +    for (port_num = 0; port_num < tpg_channels; port_num++) {
>>>>>> +            item = devm_kzalloc(csi->dev, sizeof(*item), GFP_KERNEL);
>>>>> Using devm_*alloc can be dangerous. If someone unbinds the driver, then
>>>>> all memory allocated with devm_ is immediately freed. But if an
>>>>> application
>>>>> still has a filehandle open, then when it closes it it might still
>>>>> reference
>>>>> this already-freed memory.
>>>>>
>>>>> I recommend that you avoid using devm_*alloc for media drivers.
>>>> A good test is to unbind & bind the driver:
>>>>
>>>> cd /sys/devices/platform/50000000.host1x/54080000.vi/driver
>>>> echo -n 54080000.vi >unbind
>>>> echo -n 54080000.vi >bind
>>>>
>>>> First just do this without the driver being used. That already
>>>> gives me 'list_del corruption' kernel messages (list debugging
>>>> is turned on in my kernel).
>> Will fix in v4 to use kzalloc and also proper release v4l2 to make sure
>> unbind/bind works properly.
>>
>> BTW, tegra vi and csi are registered as clients to host1x video driver.
>>
>> So, unbind and bind should be done with host1x video driver "tegra-video"
>>
>> cd /sys/devices/platform/50000000.host1x/tegra-video/driver
>> echo -n tegra-video > unbind
>> echo -n tegra-video > bind
> This still crashes with v4, at least if I am streaming with v4l2-ctl --stream-mmap.
> Is that known?
>
> It's not a big deal at this moment, just want to know if this will be looked
> at later.
>
> Regards,
>
>          Hans

Weird, I tested streaming after unbind and bind as well and don't see 
crash. Did below steps and tried several times unbind/bind as well.

./v4l2-ctl --stream-mmap --stream-count=1 -d /dev/video3
cd /sys/devices/platform/50000000.host1x/tegra-video/driver
echo -n tegra-video > unbind
sleep 1
echo -n tegra-video > bind
cd /home/ubuntu
./v4l2-ctl --stream-mmap --stream-count=1 -d /dev/video3

Can you post call trace when you saw crash?

>>>> Note that this first test is basically identical to a rmmod/modprobe
>>>> of the driver. But when I compiled the driver as a module it didn't
>>>> create any video device nodes! Nor did I see any errors in the kernel
>>>> log. I didn't pursue this, and perhaps I did something wrong, but it's
>>>> worth taking a look at.
>>>>
>>>> The next step would be to have a video node open with:
>>>>
>>>> v4l2-ctl --sleep 10
>>>>
>>>> then while it is sleeping unbind the driver and see what happens
>>>> when v4l2-ctl exits.
>>>>
>>>> Worst case is when you are streaming:
>>>>
>>>> v4l2-ctl --stream-mmap
>>>>
>>>> and then unbind.
>>>>
>>>> In general, the best way to get this to work correctly is:
>>>>
>>>> 1) don't use devm_*alloc
>>>> 2) set the release callback of struct v4l2_device and do all freeing
>>>> there.
>>>> 3) in the platform remove() callback you call media_device_unregister()
>>>>      and video_unregister_device().
>>> Reg 3, in current patch, media_device_unregister is called in
>>> host1x_video_remove
>>> video_unregister_device happens during host1x_video_remove ->
>>> host1x_device_exit -> tegra_vi_exit -> tegra_vi_channels_cleanup
>>>
>>>> It's worth getting this right in this early stage, rather than fixing it
>>>> in the future.
>>>>
>>>> Regards,
>>>>
>>>>           Hans