Messages in this thread | | | Subject | Re: [RFC PATCH v3 4/6] media: tegra: Add Tegra210 Video input driver | From | Sowjanya Komatineni <> | Date | Wed, 18 Mar 2020 10:17:12 -0700 |
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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
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