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

[Marek Szyprowski <m.szyprowski@samsung.com>]

Hi,

On 22.11.2021 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>
This fixes the issue I've reported here: 
https://lore.kernel.org/all/f3bfcbc7-f701-c74a-09bd-6491d4c8d863@samsung.com/
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
> ---
>   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)

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland