Re: [RFT PATCH] usb: hub: Fix locking issues with address0_mutex

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 11/22/21 11:50, Mathias Nyman wrote:
> Fix the circular lock dependency and unbalanced unlock of addess0_mutex
> introduced when fixing an address0_mutex enumeration retry race in commit
> ae6dc22d2d1 ("usb: hub: Fix usb enumeration issue due to address0 race")
> 
> Make sure locking order between port_dev->status_lock and address0_mutex
> is correct, and that address0_mutex is not unlocked in hub_port_connect
> "done:" codepath which may be reached without locking address0_mutex
> 
> Fixes: 6ae6dc22d2d1 ("usb: hub: Fix usb enumeration issue due to address0 race")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>

Oh, this is great, with this patch I can finally hot-plug my
thunderbolt dock (and thus a XHCI controller) without the XHCI
controller given a whole bunch of weird errors (and some USB
devices not working), which it does not when already connected at boot.

I also tried the hotplug thingy with the previous fix without
this locking fix and then I actually hit the deadlock and things
like lsusb would hang.

If we can get these 2 fixes together merged soon and also backported
to the stable series that would be great:

Acked-by: Hans de Goede <hdegoede@redhat.com>
Tested-by: Hans de Goede <hdegoede@redhat.com>

Regards,

Hans







> ---
>  drivers/usb/core/hub.c | 20 ++++++++++++--------
>  1 file changed, 12 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index 00c3506324e4..00070a8a6507 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -5188,6 +5188,7 @@ static void hub_port_connect(struct usb_hub *hub, int port1, u16 portstatus,
>  	struct usb_port *port_dev = hub->ports[port1 - 1];
>  	struct usb_device *udev = port_dev->child;
>  	static int unreliable_port = -1;
> +	bool retry_locked;
>  
>  	/* Disconnect any existing devices under this port */
>  	if (udev) {
> @@ -5244,10 +5245,10 @@ static void hub_port_connect(struct usb_hub *hub, int port1, u16 portstatus,
>  
>  	status = 0;
>  
> -	mutex_lock(hcd->address0_mutex);
> -
>  	for (i = 0; i < PORT_INIT_TRIES; i++) {
> -
> +		usb_lock_port(port_dev);
> +		mutex_lock(hcd->address0_mutex);
> +		retry_locked = true;
>  		/* reallocate for each attempt, since references
>  		 * to the previous one can escape in various ways
>  		 */
> @@ -5255,6 +5256,8 @@ static void hub_port_connect(struct usb_hub *hub, int port1, u16 portstatus,
>  		if (!udev) {
>  			dev_err(&port_dev->dev,
>  					"couldn't allocate usb_device\n");
> +			mutex_unlock(hcd->address0_mutex);
> +			usb_unlock_port(port_dev);
>  			goto done;
>  		}
>  
> @@ -5276,13 +5279,13 @@ static void hub_port_connect(struct usb_hub *hub, int port1, u16 portstatus,
>  		}
>  
>  		/* reset (non-USB 3.0 devices) and get descriptor */
> -		usb_lock_port(port_dev);
>  		status = hub_port_init(hub, udev, port1, i);
> -		usb_unlock_port(port_dev);
>  		if (status < 0)
>  			goto loop;
>  
>  		mutex_unlock(hcd->address0_mutex);
> +		usb_unlock_port(port_dev);
> +		retry_locked = false;
>  
>  		if (udev->quirks & USB_QUIRK_DELAY_INIT)
>  			msleep(2000);
> @@ -5372,11 +5375,14 @@ static void hub_port_connect(struct usb_hub *hub, int port1, u16 portstatus,
>  
>  loop_disable:
>  		hub_port_disable(hub, port1, 1);
> -		mutex_lock(hcd->address0_mutex);
>  loop:
>  		usb_ep0_reinit(udev);
>  		release_devnum(udev);
>  		hub_free_dev(udev);
> +		if (retry_locked) {
> +			mutex_unlock(hcd->address0_mutex);
> +			usb_unlock_port(port_dev);
> +		}
>  		usb_put_dev(udev);
>  		if ((status == -ENOTCONN) || (status == -ENOTSUPP))
>  			break;
> @@ -5399,8 +5405,6 @@ static void hub_port_connect(struct usb_hub *hub, int port1, u16 portstatus,
>  	}
>  
>  done:
> -	mutex_unlock(hcd->address0_mutex);
> -
>  	hub_port_disable(hub, port1, 1);
>  	if (hcd->driver->relinquish_port && !hub->hdev->parent) {
>  		if (status != -ENOTCONN && status != -ENODEV)
>