Re: [PATCH] media: rtl2832_sdr: free DMA stream buffers before clearing udev on remove

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

On 13/05/2026 07:57, Valery Borovsky wrote:
> rtl2832_sdr_remove() runs on USB disconnect and immediately clears
> dev->udev to NULL before any pending streaming teardown can run. When
> the user-space application later closes its file descriptor, vb2 calls
> rtl2832_sdr_stop_streaming() which in turn calls
> rtl2832_sdr_free_stream_bufs(). That helper releases each coherent
> buffer with:
> 
>     usb_free_coherent(dev->udev, dev->buf_size,
>                       dev->buf_list[dev->buf_num],
>                       dev->dma_addr[dev->buf_num]);
> 
> usb_free_coherent() returns immediately when its dev argument is NULL,
> so every DMA stream buffer that was live at disconnect is silently
> leaked. The URBs allocated in rtl2832_sdr_alloc_urbs() outlive the
> device for the same reason.
> 
> Tear down the streaming state in rtl2832_sdr_remove() while dev->udev
> is still valid: call rtl2832_sdr_kill_urbs(), rtl2832_sdr_free_urbs()
> and rtl2832_sdr_free_stream_bufs() before zeroing dev->udev. The
> helpers are idempotent (they clear urbs_submitted, urbs_initialized
> and the URB_BUF flag), so the subsequent stop_streaming() path from
> the vb2 release sequence becomes a safe no-op.
> 
> Issue identified by automated review of the INV-003 series at
> https://sashiko.dev/
> 
> Fixes: 771138920eaf ("[media] rtl2832_sdr: Realtek RTL2832 SDR driver module")
> Cc: stable@vger.kernel.org
> Signed-off-by: Valery Borovsky <vebohr@gmail.com>
> ---
>  drivers/media/dvb-frontends/rtl2832_sdr.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/media/dvb-frontends/rtl2832_sdr.c b/drivers/media/dvb-frontends/rtl2832_sdr.c
> index 422d1a7b5456..817d91faa598 100644
> --- a/drivers/media/dvb-frontends/rtl2832_sdr.c
> +++ b/drivers/media/dvb-frontends/rtl2832_sdr.c
> @@ -1470,6 +1470,14 @@ static void rtl2832_sdr_remove(struct platform_device *pdev)
>  
>  	mutex_lock(&dev->vb_queue_lock);
>  	mutex_lock(&dev->v4l2_lock);
> +	/*
> +	 * Release URBs and coherent DMA stream buffers while dev->udev
> +	 * is still valid; once it is cleared, usb_free_coherent() silently
> +	 * returns and any later stop_streaming() leaks the DMA memory.
> +	 */
> +	rtl2832_sdr_kill_urbs(dev);
> +	rtl2832_sdr_free_urbs(dev);
> +	rtl2832_sdr_free_stream_bufs(dev);
>  	/* No need to keep the urbs around after disconnection */
>  	dev->udev = NULL;
>  	v4l2_device_disconnect(&dev->v4l2_dev);

This isn't the right solution.

What needs to happen is that the video_unregister_device(&dev->vdev);
calls is replaced by vb2_video_unregister_device(&dev->vdev); and that
that line is moved up to before dev->udev = NULL.

vb2_video_unregister_device ensures that all streaming stops at once,
so it calls stop_streaming which will free all streaming resources.

You were on the right track, but it's not quite the right solution.

Regards,

	Hans