usb: introduce port status lock

In general we do not want khubd to act on port status changes that are
the result of 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 because usb_port_resume() was in the middle of
modifying the port status.

So, we want a new lock to hold off khubd for a given port while the
child device is being suspended, resumed, or reset.  The lock ordering
rules are now usb_lock_device() => usb_lock_port().  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-acquire it when needing to take the
device_lock.  The lock is also dropped/re-acquired during
hub_port_reconnect().

This patch also deletes hub->busy_bits as all use cases are now covered
by port PM runtime synchronization or the port->status_lock and it
pushes down usb_device_lock() into usb_remote_wakeup().

Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/usb/core/hub.h b/drivers/usb/core/hub.h
index 906c355e0631..0a7cdc0ef0a9 100644
--- a/drivers/usb/core/hub.h
+++ b/drivers/usb/core/hub.h
@@ -45,8 +45,6 @@ struct usb_hub {
 	unsigned long		event_bits[1];	/* status change bitmask */
 	unsigned long		change_bits[1];	/* ports with logical connect
 							status change */
-	unsigned long		busy_bits[1];	/* ports being reset or
-							resumed */
 	unsigned long		removed_bits[1]; /* ports with a "removed"
 							device present */
 	unsigned long		wakeup_bits[1];	/* ports that have signaled
@@ -88,6 +86,7 @@ struct usb_hub {
  * @peer: related usb2 and usb3 ports (share the same connector)
  * @connect_type: port's connect type
  * @location: opaque representation of platform connector location
+ * @status_lock: synchronize port_event() vs usb_port_{suspend|resume}
  * @portnum: port index num based one
  * @is_superspeed cache super-speed status
  */
@@ -98,6 +97,7 @@ struct usb_port {
 	struct usb_port *peer;
 	enum usb_port_connect_type connect_type;
 	usb_port_location_t location;
+	struct mutex status_lock;
 	u8 portnum;
 	unsigned int is_superspeed:1;
 };