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

[Sowjanya Komatineni]

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