Re: [PATCH v1 1/2] usb: gadget: udc: core: Invoke usb_gadget_connect only when started

Alan Stern
2023-04-06T01:29:30Z

On Wed, Apr 05, 2023 at 09:31:32AM +0000, Badhri Jagan Sridharan wrote:
> usb_udc_connect_control does not check to see if the udc
> has already been started. This causes gadget->ops->pullup
> to be called through usb_gadget_connect when invoked
> from usb_udc_vbus_handler even before usb_gadget_udc_start
> is called. Guard this by checking for udc->started in
> usb_udc_connect_control before invoking usb_gadget_connect.
>
> Guarding udc_connect_control, udc->started and udc->vbus
> with its own mutex as usb_udc_connect_control_locked
> can be simulataneously invoked from different code paths.
>
> Cc: stable@vger.kernel.org
>
> Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
> Fixes: 628ef0d273a6 ("usb: udc: add usb_udc_vbus_handler")

There's a problem with this patch.

> ---
> drivers/usb/gadget/udc/core.c | 20 ++++++++++++++++----
> 1 file changed, 16 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
> index 3dcbba739db6..890f92cb6344 100644
> --- a/drivers/usb/gadget/udc/core.c
> +++ b/drivers/usb/gadget/udc/core.c

> @@ -1140,14 +1145,18 @@ static inline int usb_gadget_udc_start(struct usb_udc *udc)
> {
> int ret;
>
> + mutex_lock(&udc_connect_control_lock);
> if (udc->started) {
> dev_err(&udc->dev, "UDC had already started\n");
> + mutex_unlock(&udc_connect_control_lock);
> return -EBUSY;
> }
>
> ret = udc->gadget->ops->udc_start(udc->gadget, udc->driver);
> if (!ret)
> udc->started = true;
> + usb_udc_connect_control_locked(udc);
> + mutex_unlock(&udc_connect_control_lock);

You moved the connect_control call up here, into usb_gadget_udc_start().

> return ret;
> }
> @@ -1165,13 +1174,17 @@ static inline int usb_gadget_udc_start(struct usb_udc *udc)
> */
> static inline void usb_gadget_udc_stop(struct usb_udc *udc)
> {
> + mutex_lock(&udc_connect_control_lock);
> if (!udc->started) {
> dev_err(&udc->dev, "UDC had already stopped\n");
> + mutex_unlock(&udc_connect_control_lock);
> return;
> }
>
> udc->gadget->ops->udc_stop(udc->gadget);
> udc->started = false;
> + usb_udc_connect_control_locked(udc);
> + mutex_unlock(&udc_connect_control_lock);
> }
>
> /**
> @@ -1527,7 +1540,6 @@ static int gadget_bind_driver(struct device *dev)
> if (ret)
> goto err_start;
> usb_gadget_enable_async_callbacks(udc);
> - usb_udc_connect_control(udc);

This is where it used to be.

The problem is that in the gadget_bind_driver pathway,
usb_gadget_enable_async_callbacks() has to run _before_ the gadget
connects. Maybe you can fix this by leaving the function call in its
original location and protecting it with the new mutex?

There may be a similar problem with disconnecting and the
gadget_unbind_driver pathway (usb_gadget_disable_async_callbacks() has to
run _after_ the disconnect occurs). I haven't tried to follow the patch
in enough detail to see whether that's an issue.

Alan Stern

>
> kobject_uevent(&udc->dev.kobj, KOBJ_CHANGE);
> return 0;
>
> base-commit: d629c0e221cd99198b843d8351a0a9bfec6c0423
> --
> 2.40.0.348.gf938b09366-goog
>