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

[Sowjanya Komatineni <skomatineni@nvidia.com>]

On 3/19/20 7:29 AM, Hans Verkuil wrote:
> External email: Use caution opening links or attachments
>
>
> On 3/18/20 6:17 PM, Sowjanya Komatineni wrote:
>> 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.
> That's indeed what I did. I don't want to try it again since I'm working from home
> and the Jetson is in the office. And once it crashes I need someone in the office
> to press the reset button. I hope I can pick it up next week to keep it at home as
> that will make testing a lot easier.

Hi Hans, no problem. I repro'd and fixed it. Will include the fix in v5.

Tested fix to make sure of no crash with unbind/bind during sleep and 
also during streaming.

during sleep, after specified time it shows below info but no crash.

Test VIDIOC_QUERYCAP:
                 VIDIOC_QUERYCAP returned -1 (No such device)
VIDIOC_QUERYCAP: No such device

Thanks

Sowjanya

>
>> Will look and have fix in v5.
> Nice!
>
> Thank you,
>
>          Hans
>
>> 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