linux-kernel - Re: [PATCH] sound: usb: get lock before calling usb_enable

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Date:   Tue, 03 Aug 2021 09:40:50 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Salah Triki <salah.triki@...il.com>
Cc:     Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
        Pavel Skripkin <paskripkin@...il.com>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Mark Brown <broonie@...nel.org>, Joe Perches <joe@...ches.com>,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sound: usb: get lock before calling  usb_enable_autosuspend()

On Tue, 03 Aug 2021 00:53:39 +0200,
Salah Triki wrote:
> 
> Based on the documentation of usb_enable_autosuspend(), the
> caller must hold udev's device lock.

The device lock is already held in the caller side (in the driver
core), hence this change will lead to a deadlock.


thanks,

Takashi

> 
> Signed-off-by: Salah Triki <salah.triki@...il.com>
> ---
>  sound/usb/card.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/sound/usb/card.c b/sound/usb/card.c
> index 2f6a62416c05..9290ba0acd5f 100644
> --- a/sound/usb/card.c
> +++ b/sound/usb/card.c
> @@ -907,8 +907,13 @@ static void usb_audio_disconnect(struct usb_interface *intf)
>  		}
>  	}
>  
> -	if (chip->quirk_type & QUIRK_SETUP_DISABLE_AUTOSUSPEND)
> -		usb_enable_autosuspend(interface_to_usbdev(intf));
> +	if (chip->quirk_type & QUIRK_SETUP_DISABLE_AUTOSUSPEND) {
> +		struct usb_device *udev = interface_to_usbdev(intf);
> +
> +		usb_lock_device(udev);
> +		usb_enable_autosuspend(udev);
> +		usb_unlock_device(udev);
> +	}
>  
>  	chip->num_interfaces--;
>  	if (chip->num_interfaces <= 0) {
> -- 
> 2.25.1
>