Re: [PATCH 0/3] Collapse vimc into single monolithic driver

["André Almeida" <andrealmeid@collabora.com>]

Hi Shuah,

On 8/12/19 11:08 AM, Shuah Khan wrote:
> On 8/9/19 9:51 PM, Helen Koike wrote:
>> Hi Andre,
>>
>> Thanks for testing this.
>>
>> On 8/9/19 9:24 PM, André Almeida wrote:
>>> On 8/9/19 9:17 PM, Shuah Khan wrote:
>>>> Hi Andre,
>>>>
>>>> On 8/9/19 5:52 PM, André Almeida wrote:
>>>>> Hello Shuah,
>>>>>
>>>>> Thanks for the patch, I did some comments below.
>>>>>
>>>>> On 8/9/19 6:45 PM, Shuah Khan wrote:
>>>>>> vimc uses Component API to split the driver into functional
>>>>>> components.
>>>>>> The real hardware resembles a monolith structure than component and
>>>>>> component structure added a level of complexity making it hard to
>>>>>> maintain without adding any real benefit.
>>>>>>       The sensor is one vimc component that would makes sense to be a
>>>>>> separate
>>>>>> module to closely align with the real hardware. It would be easier to
>>>>>> collapse vimc into single monolithic driver first and then split the
>>>>>> sensor off as a separate module.
>>>>>>
>>>>>> This patch series emoves the component API and makes minimal
>>>>>> changes to
>>>>>> the code base preserving the functional division of the code
>>>>>> structure.
>>>>>> Preserving the functional structure allows us to split the sensor off
>>>>>> as a separate module in the future.
>>>>>>
>>>>>> Major design elements in this change are:
>>>>>>       - Use existing struct vimc_ent_config and struct
>>>>>> vimc_pipeline_config
>>>>>>         to drive the initialization of the functional components.
>>>>>>       - Make vimc_ent_config global by moving it to vimc.h
>>>>>>       - Add two new hooks add and rm to initialize and register,
>>>>>> unregister
>>>>>>         and free subdevs.
>>>>>>       - All component API is now gone and bind and unbind hooks are
>>>>>> modified
>>>>>>         to do "add" and "rm" with minimal changes to just add and rm
>>>>>> subdevs.
>>>>>>       - vimc-core's bind and unbind are now register and unregister.
>>>>>>       - vimc-core invokes "add" hooks from its
>>>>>> vimc_register_devices().
>>>>>>         The "add" hooks remain the same and register subdevs. They
>>>>>> don't
>>>>>>         create platform devices of their own and use vimc's
>>>>>> pdev.dev as
>>>>>>         their reference device. The "add" hooks save their
>>>>>> vimc_ent_device(s)
>>>>>>         in the corresponding vimc_ent_config.
>>>>>>       - vimc-core invokes "rm" hooks from its unregister to
>>>>>> unregister
>>>>>> subdevs
>>>>>>         and cleanup.
>>>>>>       - vimc-core invokes "add" and "rm" hooks with pointer to struct
>>>>>> vimc_device
>>>>>>         and the corresponding struct vimc_ent_config pointer.
>>>>>>       The following configure and stream test works on all devices.
>>>>>>            media-ctl -d platform:vimc -V '"Sensor
>>>>>> A":0[fmt:SBGGR8_1X8/640x480]'
>>>>>>       media-ctl -d platform:vimc -V '"Debayer
>>>>>> A":0[fmt:SBGGR8_1X8/640x480]'
>>>>>>       media-ctl -d platform:vimc -V '"Sensor
>>>>>> B":0[fmt:SBGGR8_1X8/640x480]'
>>>>>>       media-ctl -d platform:vimc -V '"Debayer
>>>>>> B":0[fmt:SBGGR8_1X8/640x480]'
>>>>>>            v4l2-ctl -z platform:vimc -d "RGB/YUV Capture" -v
>>>>>> width=1920,height=1440
>>>>>>       v4l2-ctl -z platform:vimc -d "Raw Capture 0" -v
>>>>>> pixelformat=BA81
>>>>>>       v4l2-ctl -z platform:vimc -d "Raw Capture 1" -v
>>>>>> pixelformat=BA81
>>>>>>            v4l2-ctl --stream-mmap --stream-count=100 -d /dev/video1
>>>>>>       v4l2-ctl --stream-mmap --stream-count=100 -d /dev/video2
>>>>>>       v4l2-ctl --stream-mmap --stream-count=100 -d /dev/video3
>>>>>>
>>>>>> The third patch in the series fixes a general protection fault found
>>>>>> when rmmod is done while stream is active.
>>>>>
>>>>> I applied your patch on top of media_tree/master and I did some
>>>>> testing.
>>>>> Not sure if I did something wrong, but just adding and removing the
>>>>> module generated a kernel panic:
>>>>
>>>> Thanks for testing.
>>>>
>>>> Odd. I tested modprobe and rmmod both.I was working on Linux 5.3-rc2.
>>>> I will apply these to media latest and work from there. I have to
>>>> rebase these on top of the reverts from Lucas and Helen
>>>
>>> Ok, please let me know if I succeeded to reproduce.
>>>
>>>>>
>>>>> ~# modprobe vimc
>>>>> ~# rmmod vimc
>>>>> [   16.452974] stack segment: 0000 [#1] SMP PTI
>>>>> [   16.453688] CPU: 0 PID: 2038 Comm: rmmod Not tainted 5.3.0-rc2+ #36
>>>>> [   16.454678] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
>>>>> BIOS 1.12.0-20181126_142135-anatol 04/01/2014
>>>>> [   16.456191] RIP: 0010:kfree+0x4d/0x240
>>>>>
>>>>> <registers values...>
>>>>>
>>>>> [   16.469188] Call Trace:
>>>>> [   16.469666]  vimc_remove+0x35/0x90 [vimc]
>>>>> [   16.470436]  platform_drv_remove+0x1f/0x40
>>>>> [   16.471233]  device_release_driver_internal+0xd3/0x1b0
>>>>> [   16.472184]  driver_detach+0x37/0x6b
>>>>> [   16.472882]  bus_remove_driver+0x50/0xc1
>>>>> [   16.473569]  vimc_exit+0xc/0xca0 [vimc]
>>>>> [   16.474231]  __x64_sys_delete_module+0x18d/0x240
>>>>> [   16.475036]  do_syscall_64+0x43/0x110
>>>>> [   16.475656]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>>>> [   16.476504] RIP: 0033:0x7fceb8dafa4b
>>>>>
>>>>> <registers values...>
>>>>>
>>>>> [   16.484853] Modules linked in: vimc(-) videobuf2_vmalloc
>>>>> videobuf2_memops v4l2_tpg videobuf2_v4l2 videobuf2_common
>>>>> [   16.486187] ---[ end trace 91e5e0894e254d49 ]---
>>>>> [   16.486758] RIP: 0010:kfree+0x4d/0x240
>>>>>
>>>>> <registers values...>
>>>>>
>>>>> fish: “rmmod vimc” terminated by signal SIGSEGV (Address boundary
>>>>> error)
>>>>>
>>>>> I just added the module after booting, no other action was made.
>>>>> Here is
>>>>> how my `git log --oneline` looks like:
>>>>>
>>>>> 897d708e922b media: vimc: Fix gpf in rmmod path when stream is active
>>>>> 2e4a5ad8ad6d media: vimc: Collapse component structure into a single
>>>>> monolithic driver
>>>>> 7c8da1687e92 media: vimc: move private defines to a common header
>>>>> 97299a303532 media: Remove dev_err() usage after platform_get_irq()
>>>>> 25a3d6bac6b9 media: adv7511/cobalt: rename driver name to adv7511-v4l2
>>
>> I couldn't reproduce the error, my tree looks the same:
>>
>> [I] koike@floko ~/m/o/linux> git log --oneline
>> e3345155c8ed (HEAD) media: vimc: Fix gpf in rmmod path when stream is
>> active
>> 43e9e2fe761f media: vimc: Collapse component structure into a single
>> monolithic driver
>> 8a6d0b9adde0 media: vimc: move private defines to a common header
>> 97299a303532 (media/master) media: Remove dev_err() usage after
>> platform_get_irq()
>> 25a3d6bac6b9 media: adv7511/cobalt: rename driver name to adv7511-v4l2
> 
> Thanks Helen for trying to reproduce and sharing the result.

Me and Helen found out what is the problem. If you follow this call trace:

vimc_ent_sd_unregister()
v4l2_device_unregister_subdev()
v4l2_subdev_release()

You'll notice that this last function calls the `release` callback
implementation of the subdevice. For instance, the `release` of
vimc-sensor is this one:

static void vimc_sen_release(struct v4l2_subdev *sd)
{
	struct vimc_sen_device *vsen =
				container_of(sd, struct vimc_sen_device, sd);

	v4l2_ctrl_handler_free(&vsen->hdl);
	tpg_free(&vsen->tpg);
	kfree(vsen);
}

And then you can see that `vsen` has been freed. Back to
vimc_ent_sd_unregister(), after v4l2_device_unregister_subdev(), the
function will call vimc_pads_cleanup(). This is basically a
kfree(ved->pads), but `ved` has just been freed at
v4l2_subdev_release(), producing a memory fault.

To fix that, we found two options:

- place the kfree(ved->pads) inside the release callback of each
subdevice and removing vimc_pads_cleanup() from
vimc_ent_sd_unregister()
- use a auxiliary variable to hold the address of the pads, for instance:

void vimc_ent_sd_unregister(...)
{
    struct media_pad *pads = ved->pads;
    ...
    vimc_pads_cleanup(pads);
}


Thanks,
	André

>>
>> André, is this deterministic? Or it just happens sometimes?
>>
>>>>> ...
>>>>>
>>>>>>
>>>>>> vimc_print_dot (--print-dot) topology after this change:
>>>>>> digraph board {
>>>>>>      rankdir=TB
>>>>>>      n00000001 [label="{{} | Sensor A\n/dev/v4l-subdev0 | {<port0>
>>>>>> 0}}", shape=Mrecord, style=filled, fillcolor=green]
>>>>>>      n00000001:port0 -> n00000005:port0 [style=bold]
>>>>>>      n00000001:port0 -> n0000000b [style=bold]
>>>>>>      n00000003 [label="{{} | Sensor B\n/dev/v4l-subdev1 | {<port0>
>>>>>> 0}}", shape=Mrecord, style=filled, fillcolor=green]
>>>>>>      n00000003:port0 -> n00000008:port0 [style=bold]
>>>>>>      n00000003:port0 -> n0000000f [style=bold]
>>>>>>      n00000005 [label="{{<port0> 0} | Debayer A\n/dev/v4l-subdev2 |
>>>>>> {<port1> 1}}", shape=Mrecord, style=filled, fillcolor=green]
>>>>>>      n00000005:port1 -> n00000015:port0
>>>>>>      n00000008 [label="{{<port0> 0} | Debayer B\n/dev/v4l-subdev3 |
>>>>>> {<port1> 1}}", shape=Mrecord, style=filled, fillcolor=green]
>>>>>>      n00000008:port1 -> n00000015:port0 [style=dashed]
>>>>>>      n0000000b [label="Raw Capture 0\n/dev/video1", shape=box,
>>>>>> style=filled, fillcolor=yellow]
>>>>>>      n0000000f [label="Raw Capture 1\n/dev/video2", shape=box,
>>>>>> style=filled, fillcolor=yellow]
>>>>>>      n00000013 [label="{{} | RGB/YUV Input\n/dev/v4l-subdev4 |
>>>>>> {<port0> 0}}", shape=Mrecord, style=filled, fillcolor=green]
>>>>>>      n00000013:port0 -> n00000015:port0 [style=dashed]
>>>>>>      n00000015 [label="{{<port0> 0} | Scaler\n/dev/v4l-subdev5 |
>>>>>> {<port1> 1}}", shape=Mrecord, style=filled, fillcolor=green]
>>>>>>      n00000015:port1 -> n00000018 [style=bold]
>>>>>>      n00000018 [label="RGB/YUV Capture\n/dev/video3", shape=box,
>>>>>> style=filled, fillcolor=yellow]
>>>>>> }
>>>>>
>>>>> Since the topology changed, it would be nice to change in the
>>>>> documentation as well. The current dot file can be found at
>>>>> `Documentation/media/v4l-drivers/vimc.dot` and it's rendered at this
>>>>> page:
>>>>> https://www.kernel.org/doc/html/latest/media/v4l-drivers/vimc.html
>>>>>
>>>>
> 
> Thanks Andre! Yes this is the one I am using as a reference.
> 
>>>> Topology shouldn't have changed. No changes to links or pads etc.
>>>> I will take a look to be sure. I agree that if topology changes
>>>> document should be updated.
>>>
>>> If you "diff" the current dot with the dot you generated, you will see
>>> some differences. The main difference is that "RGB/YUV Input" was a
>>> device "/dev/video2/", and now it a subdevice "/dev/v4l-subdev4".
>>
>> hmm, I just generated the topology for media/master, and it is
>> /dev/v4l-subdev4. As we don't have an implementation of the output device
>> yet, we used the sensor as a place holder and that is why it appears as
>> "/dev/v4l-subdev4", what is in the docs is the ideal version after we get
>> the output merged. We should update the docs in any case.
>>
> 
> Helen! Does the master match what I generated. In any case, I will do
> the diff of before and after my patches for sure.
> 
> I can update the document with what it should be.
> 
> thanks,
> -- Shuah
>