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SubjectRe: [PATCH v2] usb: hub: Do not attempt to autosuspend disconnected devices
On Mon, 20 Mar 2017, Guenter Roeck wrote:

> While running a bind/unbind stress test with the dwc3 usb driver on rk3399,
> the following crash was observed.
>
> Unable to handle kernel NULL pointer dereference at virtual address 00000218
> pgd = ffffffc00165f000
> [00000218] *pgd=000000000174f003, *pud=000000000174f003,
> *pmd=0000000001750003, *pte=00e8000001751713

...

> Code analysis shows that intf is set to NULL in usb_disable_device() prior
> to setting actconfig to NULL. At the same time, usb_runtime_idle() does not
> lock the usb device, and neither does any of the functions in the
> traceback. This means that there is no protection against a race condition
> where usb_disable_device() is removing dev->actconfig->interface[] pointers
> while those are being accessed from autosuspend_check().
>
> To solve the problem, synchronize and validate device state between
> autosuspend_check() and usb_disconnect().
>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> ---
> v2: Do not disable autosuspend in usb_disconnect(). Instead, check the
> usb device state in autosuspend_check().
> In usb_disconnect(), call pm_runtime_barrier() earlier, immediately
> after changing the USB device state.
>
> drivers/usb/core/driver.c | 3 +++
> drivers/usb/core/hub.c | 7 +++++++
> 2 files changed, 10 insertions(+)
>
> diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
> index 7ebdf2a4e8fe..eb87a259d55c 100644
> --- a/drivers/usb/core/driver.c
> +++ b/drivers/usb/core/driver.c
> @@ -1781,6 +1781,9 @@ static int autosuspend_check(struct usb_device *udev)
> int w, i;
> struct usb_interface *intf;
>
> + if (udev->state == USB_STATE_NOTATTACHED)
> + return -ENODEV;
> +
> /* Fail if autosuspend is disabled, or any interfaces are in use, or
> * any interface drivers require remote wakeup but it isn't available.
> */
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index 57bb427c8878..fd80513aaeff 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -2084,6 +2084,13 @@ void usb_disconnect(struct usb_device **pdev)
> * this quiesces everything except pending urbs.
> */
> usb_set_device_state(udev, USB_STATE_NOTATTACHED);
> +
> + /*
> + * Ensure that the pm runtime code knows that the USB device
> + * is in the process of being disconnected.
> + */
> + pm_runtime_barrier(&udev->dev);
> +
> dev_info(&udev->dev, "USB disconnect, device number %d\n",
> udev->devnum);
>

Very minor nit: I would place the pm_runtime_barrier() after the
dev_info(), so that we would know the device is going away if anything
should go wrong during the barrier call.

Aside from that,

Acked-by: Alan Stern <stern@rowland.harvard.edu>

Alan Stern

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