Re: [PATCH 27/65] media: Reset file->private_data to NULL in v4l2_fh_del()

[Hans Verkuil <hverkuil+cisco@kernel.org>]

On 07/08/2025 22:25, Laurent Pinchart wrote:
> On Thu, Aug 07, 2025 at 08:00:06PM +0300, Laurent Pinchart wrote:
>> On Thu, Aug 07, 2025 at 11:50:07AM +0300, Laurent Pinchart wrote:
>>> On Wed, Aug 06, 2025 at 02:45:14PM +0200, Hans Verkuil wrote:
>>>> On 02/08/2025 11:22, Jacopo Mondi wrote:
>>>>> From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
>>>>>
>>>>> Multiple drivers that use v4l2_fh and call v4l2_fh_del() manually reset
>>>>> the file->private_data pointer to NULL in their video device .release()
>>>>> file operation handler. Move the code to the v4l2_fh_del() function to
>>>>> avoid direct access to file->private_data in drivers. This requires
>>>>> adding a file pointer argument to the function.
>>>>>
>>>>> Changes to drivers have been generated with the following coccinelle
>>>>> semantic patch:
>>>>>
>>>>> @@
>>>>> expression fh;
>>>>> identifier filp;
>>>>> identifier release;
>>>>> type ret;
>>>>> @@
>>>>> ret release(..., struct file *filp, ...)
>>>>> {
>>>>> 	<...
>>>>> -	filp->private_data = NULL;
>>>>> 	...
>>>>> -	v4l2_fh_del(fh);
>>>>> +	v4l2_fh_del(fh, filp);
>>>>> 	...>
>>>>> }
>>>>>
>>>>> @@
>>>>> expression fh;
>>>>> identifier filp;
>>>>> identifier release;
>>>>> type ret;
>>>>> @@
>>>>> ret release(..., struct file *filp, ...)
>>>>> {
>>>>> 	<...
>>>>> -	v4l2_fh_del(fh);
>>>>> +	v4l2_fh_del(fh, filp);
>>>>> 	...
>>>>> -	filp->private_data = NULL;
>>>>> 	...>
>>>>> }
>>>>>
>>>>> @@
>>>>> expression fh;
>>>>> identifier filp;
>>>>> identifier release;
>>>>> type ret;
>>>>> @@
>>>>> ret release(..., struct file *filp, ...)
>>>>> {
>>>>> 	<...
>>>>> -	v4l2_fh_del(fh);
>>>>> +	v4l2_fh_del(fh, filp);
>>>>> 	...>
>>>>> }
>>>>>
>>>>> Manual changes have been applied to Documentation/ to update the usage
>>>>> patterns, to drivers/media/v4l2-core/v4l2-fh.c to update the
>>>>> v4l2_fh_del() prototype and reset file->private_data, and to
>>>>> include/media/v4l2-fh.h to update the v4l2_fh_del() function prototype
>>>>> and its documentation.
>>>>>
>>>>> Additionally, white space issues have been fixed manually in
>>>>> drivers/usb/gadget/function/uvc_v4l2.c
>>>>>
>>>>> Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
>>>>> Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
>>>>> ---
>>>>>  Documentation/driver-api/media/v4l2-fh.rst                         | 4 ++--
>>>>>  Documentation/translations/zh_CN/video4linux/v4l2-framework.txt    | 4 ++--
>>>>>  drivers/media/pci/cx18/cx18-fileops.c                              | 4 ++--
>>>>>  drivers/media/pci/ivtv/ivtv-fileops.c                              | 4 ++--
>>>>>  drivers/media/pci/saa7164/saa7164-encoder.c                        | 2 +-
>>>>>  drivers/media/pci/saa7164/saa7164-vbi.c                            | 2 +-
>>>>>  drivers/media/platform/allegro-dvt/allegro-core.c                  | 2 +-
>>>>>  drivers/media/platform/amlogic/meson-ge2d/ge2d.c                   | 2 +-
>>>>>  drivers/media/platform/amphion/vpu_v4l2.c                          | 4 ++--
>>>>>  drivers/media/platform/chips-media/coda/coda-common.c              | 4 ++--
>>>>>  drivers/media/platform/chips-media/wave5/wave5-helper.c            | 2 +-
>>>>>  drivers/media/platform/imagination/e5010-jpeg-enc.c                | 4 ++--
>>>>>  drivers/media/platform/m2m-deinterlace.c                           | 2 +-
>>>>>  drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c               | 4 ++--
>>>>>  drivers/media/platform/mediatek/mdp/mtk_mdp_m2m.c                  | 4 ++--
>>>>>  drivers/media/platform/mediatek/mdp3/mtk-mdp3-m2m.c                | 4 ++--
>>>>>  .../media/platform/mediatek/vcodec/decoder/mtk_vcodec_dec_drv.c    | 4 ++--
>>>>>  .../media/platform/mediatek/vcodec/encoder/mtk_vcodec_enc_drv.c    | 4 ++--
>>>>>  drivers/media/platform/nvidia/tegra-vde/v4l2.c                     | 2 +-
>>>>>  drivers/media/platform/nxp/dw100/dw100.c                           | 2 +-
>>>>>  drivers/media/platform/nxp/imx-jpeg/mxc-jpeg.c                     | 4 ++--
>>>>>  drivers/media/platform/nxp/imx-pxp.c                               | 2 +-
>>>>>  drivers/media/platform/nxp/imx8-isi/imx8-isi-m2m.c                 | 2 +-
>>>>>  drivers/media/platform/nxp/mx2_emmaprp.c                           | 2 +-
>>>>>  drivers/media/platform/qcom/iris/iris_vidc.c                       | 3 +--
>>>>>  drivers/media/platform/qcom/venus/core.c                           | 2 +-
>>>>>  drivers/media/platform/renesas/rcar_fdp1.c                         | 2 +-
>>>>>  drivers/media/platform/renesas/rcar_jpu.c                          | 4 ++--
>>>>>  drivers/media/platform/renesas/vsp1/vsp1_video.c                   | 2 +-
>>>>>  drivers/media/platform/rockchip/rga/rga.c                          | 2 +-
>>>>>  drivers/media/platform/rockchip/rkvdec/rkvdec.c                    | 2 +-
>>>>>  drivers/media/platform/samsung/exynos-gsc/gsc-m2m.c                | 4 ++--
>>>>>  drivers/media/platform/samsung/exynos4-is/fimc-m2m.c               | 4 ++--
>>>>>  drivers/media/platform/samsung/s5p-g2d/g2d.c                       | 2 +-
>>>>>  drivers/media/platform/samsung/s5p-jpeg/jpeg-core.c                | 4 ++--
>>>>>  drivers/media/platform/samsung/s5p-mfc/s5p_mfc.c                   | 4 ++--
>>>>>  drivers/media/platform/st/sti/bdisp/bdisp-v4l2.c                   | 4 ++--
>>>>>  drivers/media/platform/st/sti/delta/delta-v4l2.c                   | 4 ++--
>>>>>  drivers/media/platform/st/sti/hva/hva-v4l2.c                       | 4 ++--
>>>>>  drivers/media/platform/st/stm32/dma2d/dma2d.c                      | 2 +-
>>>>>  drivers/media/platform/sunxi/sun8i-di/sun8i-di.c                   | 2 +-
>>>>>  drivers/media/platform/sunxi/sun8i-rotate/sun8i_rotate.c           | 2 +-
>>>>>  drivers/media/platform/ti/omap3isp/ispvideo.c                      | 5 ++---
>>>>>  drivers/media/platform/ti/vpe/vpe.c                                | 2 +-
>>>>>  drivers/media/platform/verisilicon/hantro_drv.c                    | 4 ++--
>>>>>  drivers/media/test-drivers/vicodec/vicodec-core.c                  | 2 +-
>>>>>  drivers/media/test-drivers/vim2m.c                                 | 2 +-
>>>>>  drivers/media/test-drivers/visl/visl-core.c                        | 2 +-
>>>>>  drivers/media/usb/pvrusb2/pvrusb2-v4l2.c                           | 3 +--
>>>>>  drivers/media/v4l2-core/v4l2-fh.c                                  | 7 ++++---
>>>>>  drivers/media/v4l2-core/v4l2-subdev.c                              | 5 ++---
>>>>>  drivers/staging/media/imx/imx-media-csc-scaler.c                   | 4 ++--
>>>>>  drivers/staging/media/meson/vdec/vdec.c                            | 2 +-
>>>>>  drivers/staging/media/sunxi/cedrus/cedrus.c                        | 2 +-
>>>>>  drivers/staging/most/video/video.c                                 | 4 ++--
>>>>>  drivers/usb/gadget/function/uvc_v4l2.c                             | 3 +--
>>>>>  include/media/v4l2-fh.h                                            | 5 ++++-
>>>>>  57 files changed, 89 insertions(+), 90 deletions(-)
>>>>>
>>>>
>>>> <snip>
>>>>
>>>>> diff --git a/drivers/media/v4l2-core/v4l2-fh.c b/drivers/media/v4l2-core/v4l2-fh.c
>>>>> index b59b1084d8cdf1b62da12879e21dbe56c2109648..df3ba9d4674bd25626cfcddc2d0cb28c233e3cc3 100644
>>>>> --- a/drivers/media/v4l2-core/v4l2-fh.c
>>>>> +++ b/drivers/media/v4l2-core/v4l2-fh.c
>>>>> @@ -67,7 +67,7 @@ int v4l2_fh_open(struct file *filp)
>>>>>  }
>>>>>  EXPORT_SYMBOL_GPL(v4l2_fh_open);
>>>>>  
>>>>> -void v4l2_fh_del(struct v4l2_fh *fh)
>>>>> +void v4l2_fh_del(struct v4l2_fh *fh, struct file *filp)
>>>>
>>>> Instead of adding a second argument, perhaps it is better to
>>>> just provide the filp pointer. After all, you can get the v4l2_fh
>>>> from filp->private_data.
>>>>
>>>> It simplifies the code a bit.
>>>
>>> That's an interesting idea. I'll give it a try.
>>
>> We end up with code like (e.g. in v4l2_fh_release(), with similar
>> constructs in lots of drivers)
>>
>> 	if (fh) {
>> 		v4l2_fh_del(filp);
>> 		v4l2_fh_exit(fh);
>> 		kfree(fh);
>> 	}
>>
>> compared to
>>
>> 	if (fh) {
>> 		v4l2_fh_del(fh, filp);
>> 		v4l2_fh_exit(fh);
>> 		kfree(fh);
>> 	}
>>
>> with the existing patch. I find the fact that v4l2_fh_del() takes a
>> different pointer than v4l2_fh_exit() a bit disturbing. If you think
>> it's better I'll drop the fh argument in v2.
> 
> I gave it a try, and looking at the function prototype, its
> documentation, the imbalance with v4l2_fh_add(), and the code in the
> callers, I think keeping both arguments would look cleaner. Please tell
> me if you feel strongly about this, I can still submit a patch to drop
> the argument. It can very easily be scripted with coccinelle and doesn't
> conflict with the rest of the series, so it could also be done later.

Looking at all the drivers that call v4l2_fh_del/exit I always see v4l2_fh_del()
directly followed by v4l2_fh_exit(). I think it would make a lot of sense to just
combine the two as a single function: v4l2_fh_del_exit(filp).

That simplifies the code and solves the imbalance.

Regards,

	Hans

> 
>>>>>  {
>>>>>  	unsigned long flags;
>>>>>  
>>>>> @@ -75,6 +75,8 @@ void v4l2_fh_del(struct v4l2_fh *fh)
>>>>>  	list_del_init(&fh->list);
>>>>>  	spin_unlock_irqrestore(&fh->vdev->fh_lock, flags);
>>>>>  	v4l2_prio_close(fh->vdev->prio, fh->prio);
>>>>> +
>>>>> +	filp->private_data = NULL;
>>>>>  }
>>>>>  EXPORT_SYMBOL_GPL(v4l2_fh_del);
>>>>>  
>>>>> @@ -94,10 +96,9 @@ int v4l2_fh_release(struct file *filp)
>>>>>  	struct v4l2_fh *fh = file_to_v4l2_fh(filp);
>>>>>  
>>>>>  	if (fh) {
>>>>> -		v4l2_fh_del(fh);
>>>>> +		v4l2_fh_del(fh, filp);
>>>>>  		v4l2_fh_exit(fh);
>>>>>  		kfree(fh);
>>>>> -		filp->private_data = NULL;
>>>>>  	}
>>>>>  	return 0;
>>>>>  }
>>>>
>>>> <snip>
>>>>
>>>>> diff --git a/include/media/v4l2-fh.h b/include/media/v4l2-fh.h
>>>>> index d8fcf49f10e09452b73499f4a9bd1285bc2835a5..5e4c761635120608e0b588e0b0daf63e69588d38 100644
>>>>> --- a/include/media/v4l2-fh.h
>>>>> +++ b/include/media/v4l2-fh.h
>>>>> @@ -114,12 +114,15 @@ int v4l2_fh_open(struct file *filp);
>>>>>   * v4l2_fh_del - Remove file handle from the list of file handles.
>>>>>   *
>>>>>   * @fh: pointer to &struct v4l2_fh
>>>>> + * @filp: pointer to &struct file associated with @fh
>>>>> + *
>>>>> + * The function resets filp->private_data to NULL.
>>>>>   *
>>>>>   * .. note::
>>>>>   *    Must be called in v4l2_file_operations->release\(\) handler if the driver
>>>>>   *    uses &struct v4l2_fh.
>>>>>   */
>>>>> -void v4l2_fh_del(struct v4l2_fh *fh);
>>>>> +void v4l2_fh_del(struct v4l2_fh *fh, struct file *filp);
>>>>>  
>>>>>  /**
>>>>>   * v4l2_fh_exit - Release resources related to a file handle.
>