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Message-ID: <Y1wd1wCLnx14QJuJ@rowland.harvard.edu>
Date: Fri, 28 Oct 2022 14:22:15 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Ray Chi <raychi@...gle.com>
Cc: gregkh@...uxfoundation.org, m.grzeschik@...gutronix.de,
albertccwang@...gle.com, pumahsu@...gle.com,
linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH RESEND v4] usb: core: stop USB enumeration if too many
retries
On Fri, Oct 28, 2022 at 06:25:05PM +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.
>
> This patch provides an attribute early_stop to limit the numbers of retries
> for each port of a hub. If a port was marked with early_stop attribute,
> unsuccessful connection attempts will fail quickly. In addition, if an
> early_stop port has failed to initialize, it will ignore all future
> connection events until early_stop attribute is clear.
>
> Signed-off-by: Ray Chi <raychi@...gle.com>
This seems basically okay, but I would have put the tests right at the
starts of the retry loops. This will make the logic much more
obviously correct.
> diff --git a/Documentation/ABI/testing/sysfs-bus-usb b/Documentation/ABI/testing/sysfs-bus-usb
> index 568103d3376e..545c2dd97ed0 100644
> --- a/Documentation/ABI/testing/sysfs-bus-usb
> +++ b/Documentation/ABI/testing/sysfs-bus-usb
> @@ -264,6 +264,17 @@ Description:
> attached to the port will not be detected, initialized,
> or enumerated.
>
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index bbab424b0d55..5510dbef3243 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -3081,6 +3081,48 @@ static int hub_port_reset(struct usb_hub *hub, int port1,
> return status;
> }
>
> +/*
> + * hub_port_stop_enumerate - stop USB enumeration or ignore port events
> + * @hub: target hub
> + * @port1: port num of the port
> + * @retries: port retries number of hub_port_init()
> + *
> + * Return:
> + * true: ignore port actions/events or give up connection attempts.
> + * false: keep original behavior.
> + *
> + * This function will be based on retries to check whether the port which is
> + * marked with early_stop attribute would stop enumeration or ignore events.
> + *
> + * Note:
> + * This function didn't change anything if early_stop is not set, and it will
> + * prevent all connection attempts when early_stop is set and the attempts of
> + * the port are more than 1.
> + */
> +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->early_stop) {
> + if (port_dev->ignore_event)
> + return true;
> +
> + /*
> + * We want unsuccessful attempts to fail quickly.
> + * Since some devices may need one failure during
> + * port initialization, we allow two tries but no
> + * more.
> + */
> + if (retries < 1)
Change "< 1" to "< 2". This is in better agreement with the comment,
which will make it easier for readers to understand.
> + return false;
> +
> + port_dev->ignore_event = 1;
> + } else
> + port_dev->ignore_event = 0;
> +
> + return port_dev->ignore_event;
> +}
> +
> /* Check if a port is power on */
> int usb_port_is_power_on(struct usb_hub *hub, unsigned int portstatus)
> {
> @@ -4855,6 +4897,11 @@ hub_port_init(struct usb_hub *hub, struct usb_device *udev, int port1,
> buf->bMaxPacketSize0;
> kfree(buf);
>
> + if (r < 0 && hub_port_stop_enumerate(hub, port1, retries)) {
> + retval = r;
> + goto fail;
> + }
Then instead of putting this here, put:
if (hub_port_stop_enumerate(hub, port1, retries)) {
retval = -ENODEV;
break;
}
at line 4799.
> +
> retval = hub_port_reset(hub, port1, udev, delay, false);
> if (retval < 0) /* error or disconnect */
> goto fail;
> @@ -5387,6 +5434,9 @@ 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;
And instead of putting this here, at line 5249 put:
if (hub_port_stop_enumerate(hub, port1, i)) {
status = -ENODEV;
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 +5664,10 @@ static void port_event(struct usb_hub *hub, int port1)
> if (!pm_runtime_active(&port_dev->dev))
> return;
>
> + /* skip port actions if ignore_event is true*/
> + if (hub_port_stop_enumerate(hub, port1, 0))
> + return;
The relation between the comment and the code isn't obvious. Instead,
do:
/* Skip initialization and enumeration if ignore_event is true */
if (port_dev->ignore_event)
return;
(Notice the space character you left out at the end of the comment.)
> +
> if (hub_handle_remote_wakeup(hub, port1, portstatus, portchange))
> connect_change = 1;
>
> @@ -5934,6 +5988,9 @@ 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;
And instead of putting this here, at line 5930 put:
if (hub_port_stop_enumerate(parent_hub, port1, i)) {
ret = -ENODEV;
break;
}
Alan Stern
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