Date:   Mon, 12 Aug 2019 13:10:13 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     André Almeida <andrealmeid@...labora.com>,
        Helen Koike <helen.koike@...labora.com>, mchehab@...nel.org,
        hverkuil@...all.nl, laurent.pinchart@...asonboard.com
Cc:     linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        kernel@...labora.com, Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH 0/3] Collapse vimc into single monolithic driver

On 8/12/19 12:52 PM, André Almeida wrote:
> 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@...ko ~/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);
> }
> 
> 

I fixed a problem in the thirds patch. vimc-capture uses the first
approach - placing the kfree(ved->pads) inside the release callback.

I am debugging another such problem in unbind path while streaming.
I am working on v2 and I will look for the rmmod problem and fix it.

thanks again for testing and finding the root cause.
-- Shuah

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