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Subject: Re: [PATCH 0/3] Collapse vimc into single monolithic driver
To:     Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Helen Koike <helen.koike@collabora.com>
Cc:     =?UTF-8?Q?Andr=c3=a9_Almeida?= <andrealmeid@collabora.com>,
        mchehab@kernel.org, hverkuil@xs4all.nl,
        linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
        kernel@collabora.com, Shuah Khan <skhan@linuxfoundation.org>
References: <4e9b8eb3-23c5-62ea-07dc-b51acb238dee@linuxfoundation.org>
 <15badf5e-49fa-7fbe-de6b-296e9a7f5cd9@collabora.com>
 <e21d38a5-4fcd-7b02-f5f2-e445c280f769@collabora.com>
 <2ee23903-8e99-a0a0-619a-be5bdaa71802@linuxfoundation.org>
 <374574f2-0ecd-723a-4a66-c190332aaa04@collabora.com>
 <737dbfd4-8e86-289b-1827-736e3d6ffff5@linuxfoundation.org>
 <03b51b1e-3d78-72e6-3b3e-210b4411c897@linuxfoundation.org>
 <e81df4a5-2393-e341-258c-abf55babe519@collabora.com>
 <20190813095654.GA5009@pendragon.ideasonboard.com>
 <a0fa05d7-5fc2-071a-f5ab-788662ecc6b2@collabora.com>
 <20190813123653.GE5009@pendragon.ideasonboard.com>
From:   Shuah Khan <skhan@linuxfoundation.org>
Message-ID: <f19ed1d5-76f5-0261-d857-94e08385aeea@linuxfoundation.org>
Date:   Tue, 13 Aug 2019 17:22:48 -0600
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On 8/13/19 6:36 AM, Laurent Pinchart wrote:
> Hi Helen,
> 
> On Tue, Aug 13, 2019 at 09:25:01AM -0300, Helen Koike wrote:
>> On 8/13/19 6:56 AM, Laurent Pinchart wrote:
>>> On Mon, Aug 12, 2019 at 08:41:33PM -0300, Helen Koike wrote:
>>>> On 8/12/19 7:14 PM, Shuah Khan wrote:
>>>>> On 8/12/19 1:10 PM, Shuah Khan wrote:
>>>>>> On 8/12/19 12:52 PM, André Almeida wrote:
>>>>>>> On 8/12/19 11:08 AM, Shuah Khan wrote:
>>>>>>>> On 8/9/19 9:51 PM, Helen Koike wrote:
>>>>>>>>> On 8/9/19 9:24 PM, André Almeida wrote:
>>>>>>>>>> On 8/9/19 9:17 PM, Shuah Khan wrote:
>>>>>>>>>>> On 8/9/19 5:52 PM, André Almeida wrote:
>>>>>>>>>>>> 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);
>>>>>>> }
>>>>>>>
>>>>>>>
>>>>>>
>>>>>> 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
>>>>>
>>>>> Hi Andre,
>>>>>
>>>>> Here is what's happening.
>>>>>
>>>>> Before this change, you can't really do rmmod vimc, because vimc is in
>>>>> use by other component drivers. With the collapse, now you can actually
>>>>> do rmmod on vimc and this problem in vimc_ent_sd_unregister() that frees
>>>>> pads first and the does v4l2_device_unregister_subdev().
>>>>>
>>>>> I fixed this in the 3/3 patch. I can reproduce the problem with patches 1 and 2, and patch 3 fixes it.
>>>>>
>>>>> Did you test with the third patch in this series?
>>>>
>>>> yes, we tested with 3/3, but the new problem now is when doing the following
>>>> in this order:
>>>>
>>>>      v4l2_device_unregister_subdev(sd);
>>>>      vimc_pads_cleanup(ved->pads);
>>>>
>>>>
>>>> v4l2_device_unregister_subdev() calls the release function of the subdevice that
>>>> frees the ved object, so ved->pads is not valid anymore. That is why André suggested
>>>> a temporary variable to hold ved->pads and to be able to free it later:
>>>>
>>>>      struct media_pad *pads = ved->pads;
>>>>
>>>>      v4l2_device_unregister_subdev(sd);
>>>>      vimc_pads_cleanup(pads); // So we don't use the ved object here anymore.
>>>
>>> Can't you simply call vimc_pads_cleanup() in the release function of the
>>> subdevice before freeing the ved object ?
>>
>> Yes we can, that is the other option Andre suggested.
>> The  advantage of doing it inside vimc_ent_sd_unregister() is that
>> who allocated the memory in the first place was vimc_ent_sd_register(), and also,
>> this is a common code to all subdevs, so letting it in vimc_ent_sd_unregister()
>> will make sure no subdevs ever forget to free this memory.
>> But saving the pointer to a variable to free it later is not that pretty
>> either.
> 
> The release function of a subdevice is meant to be used as a destructor,
> it should free all the resources allocated for the subdevice. Your
> subdevices (such as vimc_sca_device) are essentially objects derived
> from a common vimc subdevice object (vimc_ent_device), I thus suggest
> providing four functions to deal with vimc_ent_device:
> 
> - vimc_ent_sd_init() to initialise the base vimc_ent_device object (most
>    of the code is currently in vimc_ent_sd_register()), to be called by
>    the init function of each subdevice type (the bind functions in the
>    current code)
> 
> - vimc_ent_sd_register() to only register the vimc_ent_device once it
>    has been fully initialised
> 
> - vimc_end_sd_unregister() to unregister the vimc_ent_device
> 
> - vimc_end_sd_cleanup() to free the resources allocated by
>    vimc_ent_sd_init() (including calling vimc_pads_cleanup()), to be
>    called by the subdevice release handler
> 

We kind of mostly there. We have release handlers free'ing resources
with an exception of pads. I changed the release handlers to release
pads and with a comment where pads_init is called to say that pads
should be released from the release handler.

vimc-capture does this already. I changed the rest. rmmod works with
no issues now. rmmod when streaming comes back with in use.

There is one outstanding issue remaining in unbind path. I will fix
that in a separate patch. I decided to collapse the first two patches
into one and added common defines (vimc_device and vimc_ent_config) to
vimc-common.h based on our discussion.

I will send the patch series out soon.

thanks,
-- Shuah


thanks,
-- Shuah