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

[Sowjanya Komatineni <skomatineni@nvidia.com>]

On 3/18/20 9:25 AM, Sowjanya Komatineni wrote:
>
> On 3/18/20 9:14 AM, Sowjanya Komatineni wrote:
>>
>> 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?
>
> Tried unbind when  node is open with v4l2-ctl --sleep 10 as well and 
> bind back.
>
> I don't see crash. Will confirm on doing unbind/bind with stream-mmap...
>
Able to repro when unbind/bind happens while stream-mmap.

Will look and have fix in v5.

Thanks Hans.

>>
>>>>>> 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