Re: [PATCH 2/2] ALSA: caiaq: take a reference on the USB device in create_card()

[Takashi Iwai <tiwai@suse.de>]

On Fri, 10 Apr 2026 06:59:04 +0200,
Berk Cem Goksel wrote:
> 
> The caiaq driver stores a pointer to the parent USB device in
> cdev->chip.dev but never takes a reference on it. The card's
> private_free callback, snd_usb_caiaq_card_free(), can run
> asynchronously via snd_card_free_when_closed() after the USB
> device has already been disconnected and freed, so any access to
> cdev->chip.dev in that path dereferences a freed usb_device.
> 
> On top of the refcounting issue, the current card_free implementation
> calls usb_reset_device(cdev->chip.dev). A reset in a free callback
> is inappropriate: the device is going away, the call takes the
> device lock in a teardown context, and the reset races with the
> disconnect path that the callback is already cleaning up after.
> 
> Take a reference on the USB device in create_card() with
> usb_get_dev(), drop it with usb_put_dev() in the free callback,
> and remove the usb_reset_device() call.
> 
> Fixes: 523f1dce7096 ("ALSA: snd-usb-caiaq: add support for NI Audio Kontrol 1")
> Cc: stable@vger.kernel.org
> Cc: Andrey Konovalov <andreyknvl@gmail.com>
> Signed-off-by: Berk Cem Goksel <berkcgoksel@gmail.com>
> ---
>  sound/usb/caiaq/device.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/sound/usb/caiaq/device.c b/sound/usb/caiaq/device.c
> --- a/sound/usb/caiaq/device.c
> +++ b/sound/usb/caiaq/device.c
> @@ -385,7 +385,8 @@
>  	snd_usb_caiaq_input_free(cdev);
>  #endif
>  	snd_usb_caiaq_audio_free(cdev);
> -	usb_reset_device(cdev->chip.dev);
> +	if (cdev->chip.dev)
> +		usb_put_dev(cdev->chip.dev);

usb_put_dev() itself has a NULL check, so you can pass as is, too.
And, the Fixes tag is incorrect in this patch, too.


thanks,

Takashi

>  }
> 
>  static int create_card(struct usb_device *usb_dev,
> @@ -411,7 +412,7 @@
>  		return err;
> 
>  	cdev = caiaqdev(card);
> -	cdev->chip.dev = usb_dev;
> +	cdev->chip.dev = usb_get_dev(usb_dev);
>  	cdev->chip.card = card;
>  	cdev->chip.usb_id = USB_ID(le16_to_cpu(usb_dev->descriptor.idVendor),
>  				  le16_to_cpu(usb_dev->descriptor.idProduct));