linux-kernel - Re: [PATCH] media: usbtv: Remove useless locks in usbtv_video

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Message-ID: <CAAFQd5DR5z7xhXrnHc94FVY9Si9KWW2gYH+=Ov3yT1HMUpjhzg@mail.gmail.com>
Date: Tue, 20 Feb 2024 19:42:47 +0900
From: Tomasz Figa <tfiga@...omium.org>
To: Benjamin Gaignard <benjamin.gaignard@...labora.com>
Cc: mchehab@...nel.org, hverkuil-cisco@...all.nl, linux-media@...r.kernel.org, 
	linux-kernel@...r.kernel.org, kernel@...labora.com
Subject: Re: [PATCH] media: usbtv: Remove useless locks in usbtv_video_free()

On Tue, Feb 20, 2024 at 5:06 PM Benjamin Gaignard
<benjamin.gaignard@...labora.com> wrote:
>
> Remove locks calls in usbtv_video_free() because
> are useless and may led to a deadlock as reported here:
> https://syzkaller.appspot.com/x/bisect.txt?x=166dc872180000
>
> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...labora.com>
> Fixes: c838530d230b ("media: media videobuf2: Be more flexible on the number of queue stored buffers")
> ---
>  drivers/media/usb/usbtv/usbtv-video.c | 6 ------
>  1 file changed, 6 deletions(-)
>
> diff --git a/drivers/media/usb/usbtv/usbtv-video.c b/drivers/media/usb/usbtv/usbtv-video.c
> index 62a583040cd4..96276358d116 100644
> --- a/drivers/media/usb/usbtv/usbtv-video.c
> +++ b/drivers/media/usb/usbtv/usbtv-video.c
> @@ -963,15 +963,9 @@ int usbtv_video_init(struct usbtv *usbtv)
>
>  void usbtv_video_free(struct usbtv *usbtv)
>  {
> -       mutex_lock(&usbtv->vb2q_lock);
> -       mutex_lock(&usbtv->v4l2_lock);
> -
>         usbtv_stop(usbtv);
>         vb2_video_unregister_device(&usbtv->vdev);
>         v4l2_device_disconnect(&usbtv->v4l2_dev);
>
> -       mutex_unlock(&usbtv->v4l2_lock);
> -       mutex_unlock(&usbtv->vb2q_lock);
> -
>         v4l2_device_put(&usbtv->v4l2_dev);
>  }
> --
> 2.40.1
>

>From looking at the code in related vb2 functions and how the uvc
driver handles the cleanup, these locks shouldn't be necessary indeed,
but it would be good if someone could test this.

Reviewed-by: Tomasz Figa <tfiga@...omium.org>

Best regards,
Tomasz