On Fri, 31 Jan 2014, Dan Williams wrote:
> In general we do not want khubd to act on port status changes that are
> the result of in progress resets or port pm runtime operations.
The nomenclature is a little confusing. Let's agree that "port runtime
PM operations" will refer to usb_port_runtime_suspend/resume, and "USB
runtime PM operations" will refer to usb_port_suspend/resume. So now
this should say "in-progress resets or USB runtime PM operations".
> Specifically port power control testing has been able to trigger an
> unintended disconnect in hub_port_connect_change(), paraphrasing:
>
> if ((portstatus & USB_PORT_STAT_CONNECTION) && udev &&
> udev->state != USB_STATE_NOTATTACHED) {
> if (portstatus & USB_PORT_STAT_ENABLE) {
> /* Nothing to do */
> } else if (udev->state == USB_STATE_SUSPENDED &&
> udev->persist_enabled) {
> ...
> } else {
> /* Don't resuscitate */;
> }
> }
>
> ...by falling to the "Don't resuscitate" path or missing
> USB_PORT_STAT_CONNECTION becuase usb_port_resume() was in the middle of
> modifying the port status.
>
> The lock ordering rules are now usb_lock_device() => usb_lock_port().
Maybe you should mention the fact that you're introducing a new lock
before describing the ordering rule.
> This is mandated by the device core which may hold the device_lock on
> the usb_device before invoking usb_port_{suspend|resume} which in turn
> take the status_lock on the usb_port. We attempt to hold the
> status_lock for the duration of a port_event() run, and drop/re-aquire
> it when needing to take the device_lock.
This patch should eliminate hub->busy_bits. That field is unnecessary
now that we have real mutual exlusion for port-status operations.
> @@ -4371,17 +4389,21 @@ hub_power_remaining (struct usb_hub *hub)
> * usb_reset_and_verify_device() encounters changed descriptors (as from
> * a firmware download)
> * caller already locked the hub
> + *
> + * It assumes the port is locked on entry and arranges for it to be
> + * always unlocked on exit
I don't really like this, but I guess it's okay.
> */
> -static void hub_port_connect_change(struct usb_hub *hub, int port1,
> - u16 portstatus, u16 portchange)
> +static void hub_port_connect_change_unlock(struct usb_hub *hub, int port1,
> + u16 portstatus, u16 portchange)
You should add sparse annotations stating that this routine will unlock
and lock port_dev in unexpected ways. (If there's any way to do that;
you may also have to tell sparse that usb_{un}lock_port is an
{un}locking operation.)
> @@ -4639,9 +4671,11 @@ static int hub_handle_remote_wakeup(struct usb_hub
> *hub, unsigned int port,
> /* TRSMRCY = 10 msec */
> msleep(10);
>
> + usb_unlock_port(port_dev);
> usb_lock_device(udev);
> ret = usb_remote_wakeup(udev);
> usb_unlock_device(udev);
> + usb_lock_port(port_dev);
These things mean hub_handle_remote_wakeup needs the sparse annotations
too.
Come to think of it, you can now move the device locking down into
usb_remote_wakeup. You could also move the port unlocking down there,
if you passed port_dev as an additional argument. (It would have to be
NULL in the call from hcd_resume_work.)
> @@ -4731,7 +4765,13 @@ static void port_event(struct usb_hub *hub, int port1)
> /* take port actions that require the port to be powered on */
> pm_runtime_get_noresume(&port_dev->dev);
> pm_runtime_barrier(&port_dev->dev);
> - if (pm_runtime_active(&port_dev->dev)) {
> + usb_lock_port(port_dev);
> + do if (pm_runtime_active(&port_dev->dev)) {
Please just use a normal "if" statement.
> + /* re-read portstatus now that we are in-sync with
> + * usb_port_{suspend|resume}
> + */
> + if (hub_port_status(hub, port1, &portstatus, &portchange) < 0)
> + break;
For the most part, neither the pm_runtime_barrier nor the usb_lock_port
will have to wait. It seems unreasonable to read the port status a
second time when there's no need.
Why not put the pm_runtime_get_noresume, pm_runtime_barrier, and
usb_lock_port calls at the start of this subroutine, just before the
first call to hub_port_status? Patch 9 could be altered accordingly.
> @@ -4751,17 +4791,22 @@ static void port_event(struct usb_hub *hub, int port1)
> if (status < 0)
> hub_port_disable(hub, port1, 1);
> } else {
> + usb_unlock_port(port_dev);
> usb_lock_device(udev);
> status = usb_reset_device(udev);
> usb_unlock_device(udev);
> + usb_lock_port(port_dev);
Sparse annotations.
You forgot to acquire the port lock in usb_reset_device. The lock and
unlock calls should surround the call to usb_reset_and_verify_device.
Both that routine and hub_port_init should be documented as requiring
their caller to hold the port lock.
Alan Stern
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