USB: mutual exclusion for resetting a hub and power-managing a port

The USB core doesn't properly handle mutual exclusion between
resetting a hub and changing the power states of the hub's ports.  We
need to avoid sending port-power requests to the hub while it is being
reset, because such requests cannot succeed.

This patch fixes the problem by keeping track of when a reset is in
progress.  At such times, attempts to suspend (power-off) a port will
fail immediately with -EBUSY, and calls to usb_port_runtime_resume()
will update the power_is_on flag and return immediately.  When the
reset is complete, hub_activate() will automatically restore each port
to the proper power state.
Signed-off-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>

drivers/usb/core/hub.c

@@ -1276,12 +1276,22 @@ static void hub_quiesce(struct usb_hub *hub, enum hub_quiescing_type type)
 		flush_work(&hub->tt.clear_work);
 }
 
+static void hub_pm_barrier_for_all_ports(struct usb_hub *hub)
+{
+	int i;
+
+	for (i = 0; i < hub->hdev->maxchild; ++i)
+		pm_runtime_barrier(&hub->ports[i]->dev);
+}
+
 /* caller has locked the hub device */
 static int hub_pre_reset(struct usb_interface *intf)
 {
 	struct usb_hub *hub = usb_get_intfdata(intf);
 
 	hub_quiesce(hub, HUB_PRE_RESET);
+	hub->in_reset = 1;
+	hub_pm_barrier_for_all_ports(hub);
 	return 0;
 }
 
@@ -1290,6 +1300,8 @@ static int hub_post_reset(struct usb_interface *intf)
 {
 	struct usb_hub *hub = usb_get_intfdata(intf);
 
+	hub->in_reset = 0;
+	hub_pm_barrier_for_all_ports(hub);
 	hub_activate(hub, HUB_POST_RESET);
 	return 0;
 }

drivers/usb/core/hub.h

@@ -66,6 +66,7 @@ struct usb_hub {
 	unsigned		limited_power:1;
 	unsigned		quiescing:1;
 	unsigned		disconnected:1;
+	unsigned		in_reset:1;
 
 	unsigned		quirk_check_port_auto_suspend:1;
 

drivers/usb/core/port.c

@@ -81,6 +81,10 @@ static int usb_port_runtime_resume(struct device *dev)
 
 	if (!hub)
 		return -EINVAL;
+	if (hub->in_reset) {
+		port_dev->power_is_on = 1;
+		return 0;
+	}
 
 	usb_autopm_get_interface(intf);
 	set_bit(port1, hub->busy_bits);
@@ -117,6 +121,8 @@ static int usb_port_runtime_suspend(struct device *dev)
 
 	if (!hub)
 		return -EINVAL;
+	if (hub->in_reset)
+		return -EBUSY;
 
 	if (dev_pm_qos_flags(&port_dev->dev, PM_QOS_FLAG_NO_POWER_OFF)
 			== PM_QOS_FLAGS_ALL)