Re: [Patch v3] usb: core: stop USB enumeration if too many retries

Alan Stern
2022-09-22T15:15:25Z

Sorry I forgot about this patch.

On Thu, Sep 22, 2022 at 02:06:51PM +0200, Greg KH wrote:
> On Thu, Sep 08, 2022 at 06:40:19PM +0800, Ray Chi wrote:
> > When a broken USB accessory connects to a USB host, usbcore might
> > keep doing enumeration retries. If the host has a watchdog mechanism,
> > the kernel panic will happen on the host.
> >
> > The patch provide a attribute to limit the numbers of retries and
> > timeout lengths.
>
> This is per-port, right? Please say that here.

Also, the patch does not limit any timeout lengths -- just the number of
retries. Maybe you want to make it limit the timeouts also.

> > In addition, it also adds a function to stop the
> > port initialization and ignore events on the port if the broken
> > accessory is still connected.
>
> So this should be 2 patches? Remember, only do one logical thing per
> patch please.

The "adding a function" part is unimportant; we can see the function
simply by reading the patch. The main points here, which you have not
explained clearly, are:

1. If a port is marked with the quick_init attribute, unsuccessful
connection attempts will fail quickly.

2. Once a quick_init port has failed to initialize, it will ignore
all future connections until the quick_init attribute is turned
off.

> > Signed-off-by: Ray Chi <raychi@google.com>
> > ---
> > Changes since v2:
> > - replace the quirk with the attribute
> > - Document the attribute
> > - modify hub_port_stop_enumerate() position in port_event()
> > - modify the changelog
> >
> > Changes since v1:
> > - remove usb_hub_set_port_power()
> > - add a variable ignore_connect into struct port_dev
> > - modify hub_port_stop_enumerate() and set ignore_connect in
> > this function
> > - avoid calling hub_port_connect_change() in port_event()
> > ---
> > Documentation/ABI/testing/sysfs-bus-usb | 9 ++++++
> > drivers/usb/core/hub.c | 39 +++++++++++++++++++++++++
> > drivers/usb/core/hub.h | 4 +++
> > drivers/usb/core/port.c | 23 +++++++++++++++
> > 4 files changed, 75 insertions(+)
> >
> > diff --git a/Documentation/ABI/testing/sysfs-bus-usb b/Documentation/ABI/testing/sysfs-bus-usb
> > index 568103d3376e..d44c8aaef929 100644
> > --- a/Documentation/ABI/testing/sysfs-bus-usb
> > +++ b/Documentation/ABI/testing/sysfs-bus-usb
> > @@ -264,6 +264,15 @@ Description:
> > attached to the port will not be detected, initialized,
> > or enumerated.
> >
> > +What: /sys/bus/usb/devices/.../<hub_interface>/port<X>/quick_init
> > +Date: Sep 2022
> > +Contact: Ray Chi <raychi@google.com>
> > +Description:
> > + Some USB hosts have some watchdog mechanisms so that the device
> > + may enter ramdump if it takes a long time during port initialization.
> > + This attribute limits the numbers of retries and timeout lengths once
> > + an initialization of the port meets failures.
>
> The text here is very odd, maybe it's just a translation issue. A port
> can not "meet" a failure. And this really has nothing to do with any
> watchdog, it's just a "we want to fail broken devices quickly instead of
> giving them lots of time to connect" type of issue, right?
>
> And we already have different init schemes, "quick" is an odd way to
> phrase this, but I can't think of anything else at the moment.

"fail-fast" gives the idea better, but it's more awkward.

> > +
> > What: /sys/bus/usb/devices/.../power/usb2_lpm_l1_timeout
> > Date: May 2013
> > Contact: Mathias Nyman <mathias.nyman@linux.intel.com>
> > diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> > index d4b1e70d1498..f22caa133274 100644
> > --- a/drivers/usb/core/hub.c
> > +++ b/drivers/usb/core/hub.c
> > @@ -3081,6 +3081,29 @@ static int hub_port_reset(struct usb_hub *hub, int port1,
> > return status;
> > }
> >
> > +/* Check whether a hub would stop enumeration or ignore events on the port. */
>
> Based on what? Retries? Time of day? Phase of moon? :)
>
> > +static bool hub_port_stop_enumerate(struct usb_hub *hub, int port1, int retries)
> > +{
> > + struct usb_port *port_dev = hub->ports[port1 - 1];
> > +
> > + if (port_dev->quick_init) {
> > + if (port_dev->ignore_connect)
> > + return true;
> > +
> > + /*
> > + * Since some normal devices will be timeout in the first attempt,
> > + * set the condition to half of the retries
> > + */
> > + if (retries < (PORT_INIT_TRIES - 1) / 2)
> > + return false;

This is not a good test. You shouldn't rely on PORT_INIT_TRIES having
any particular value or being used in any particular way. You should
just something like:

/*
* We want unsuccessful attempts to fail quickly.
* Therefore allow three tries but no more.
*/
if (retries < 3)

> > +
> > + port_dev->ignore_connect = true;
> > + } else
> > + port_dev->ignore_connect = false;
>
> So this function modifies a port_dev value, AND returns it to the
> caller? Why not document that somewhere? Why do both?
>
> And if quick_init is false then it always set ignore_connect to false
> and returns false always?

As mentioned above, the goal is to limit the number of retries if
quick_init is set and prevent all connection attempts once one has
failed, without changing anything if quick_init is not set.

>
> > +
> > + return port_dev->ignore_connect;
> > +}
> > +
> > /* Check if a port is power on */
> > int usb_port_is_power_on(struct usb_hub *hub, unsigned int portstatus)
> > {
> > @@ -4855,6 +4878,11 @@ hub_port_init(struct usb_hub *hub, struct usb_device *udev, int port1,
> > buf->bMaxPacketSize0;
> > kfree(buf);
> >
> > + if (r < 0 && port_dev->quick_init) {
> > + retval = r;
> > + goto fail;

I still think you should test hub_port_stop_enumeration() here. It
doesn't make sense that you allow a few retries for other types of
errors but not for this one.

Alan Stern

> > + }
> > +
> > retval = hub_port_reset(hub, port1, udev, delay, false);
> > if (retval < 0) /* error or disconnect */
> > goto fail;
> > @@ -5387,6 +5415,9 @@ static void hub_port_connect(struct usb_hub *hub, int port1, u16 portstatus,
> > if ((status == -ENOTCONN) || (status == -ENOTSUPP))
> > break;
> >
> > + if (hub_port_stop_enumerate(hub, port1, i))
> > + break;
> > +
> > /* When halfway through our retry count, power-cycle the port */
> > if (i == (PORT_INIT_TRIES - 1) / 2) {
> > dev_info(&port_dev->dev, "attempt power cycle\n");
> > @@ -5614,6 +5645,9 @@ static void port_event(struct usb_hub *hub, int port1)
> > if (!pm_runtime_active(&port_dev->dev))
> > return;
> >
> > + if (hub_port_stop_enumerate(hub, port1, 0))
> > + return;
> > +
> > if (hub_handle_remote_wakeup(hub, port1, portstatus, portchange))
> > connect_change = 1;
> >
> > @@ -5934,6 +5968,9 @@ static int usb_reset_and_verify_device(struct usb_device *udev)
> > ret = hub_port_init(parent_hub, udev, port1, i);
> > if (ret >= 0 || ret == -ENOTCONN || ret == -ENODEV)
> > break;
> > +
> > + if (hub_port_stop_enumerate(parent_hub, port1, i))
> > + goto stop_enumerate;
> > }
> > mutex_unlock(hcd->address0_mutex);
> >
> > @@ -6022,6 +6059,8 @@ static int usb_reset_and_verify_device(struct usb_device *udev)
> > udev->bos = bos;
> > return 0;
> >
> > +stop_enumerate:
> > + mutex_unlock(hcd->address0_mutex);
> > re_enumerate:
> > usb_release_bos_descriptor(udev);
> > udev->bos = bos;
> > diff --git a/drivers/usb/core/hub.h b/drivers/usb/core/hub.h
> > index b2925856b4cb..57995ec3af58 100644
> > --- a/drivers/usb/core/hub.h
> > +++ b/drivers/usb/core/hub.h
> > @@ -90,6 +90,8 @@ struct usb_hub {
> > * @is_superspeed cache super-speed status
> > * @usb3_lpm_u1_permit: whether USB3 U1 LPM is permitted.
> > * @usb3_lpm_u2_permit: whether USB3 U2 LPM is permitted.
> > + * @ignore_connect: ignore the connection or not.
>
> Which connection? Any future connection? Or the one that is currently
> connected?
>
> > + * @quick_init: limit the numbers of retries for port initialization
>
> Limit it to what?
>
> > */
> > struct usb_port {
> > struct usb_device *child;
> > @@ -103,6 +105,8 @@ struct usb_port {
> > u32 over_current_count;
> > u8 portnum;
> > u32 quirks;
> > + bool ignore_connect;
> > + bool quick_init;
>
> Why are these bool, when:
>
> > unsigned int is_superspeed:1;
> > unsigned int usb3_lpm_u1_permit:1;
> > unsigned int usb3_lpm_u2_permit:1;
>
> Those are all bits?
>
> Be consistent please.
>
> thanks,
>
> greg k-h