USB: dummy-hcd: Fix deadlock caused by disconnect detection

The dummy-hcd driver calls the gadget driver's disconnect callback
under the wrong conditions.  It should invoke the callback when Vbus
power is turned off, but instead it does so when the D+ pullup is
turned off.

This can cause a deadlock in the composite core when a gadget driver
is unregistered:

[   88.361471] ============================================
[   88.362014] WARNING: possible recursive locking detected
[   88.362580] 4.14.0-rc2+ #9 Not tainted
[   88.363010] --------------------------------------------
[   88.363561] v4l_id/526 is trying to acquire lock:
[   88.364062]  (&(&cdev->lock)->rlock){....}, at: [<ffffffffa0547e03>] composite_disconnect+0x43/0x100 [libcomposite]
[   88.365051]
[   88.365051] but task is already holding lock:
[   88.365826]  (&(&cdev->lock)->rlock){....}, at: [<ffffffffa0547b09>] usb_function_deactivate+0x29/0x80 [libcomposite]
[   88.366858]
[   88.366858] other info that might help us debug this:
[   88.368301]  Possible unsafe locking scenario:
[   88.368301]
[   88.369304]        CPU0
[   88.369701]        ----
[   88.370101]   lock(&(&cdev->lock)->rlock);
[   88.370623]   lock(&(&cdev->lock)->rlock);
[   88.371145]
[   88.371145]  *** DEADLOCK ***
[   88.371145]
[   88.372211]  May be due to missing lock nesting notation
[   88.372211]
[   88.373191] 2 locks held by v4l_id/526:
[   88.373715]  #0:  (&(&cdev->lock)->rlock){....}, at: [<ffffffffa0547b09>] usb_function_deactivate+0x29/0x80 [libcomposite]
[   88.374814]  #1:  (&(&dum_hcd->dum->lock)->rlock){....}, at: [<ffffffffa05bd48d>] dummy_pullup+0x7d/0xf0 [dummy_hcd]
[   88.376289]
[   88.376289] stack backtrace:
[   88.377726] CPU: 0 PID: 526 Comm: v4l_id Not tainted 4.14.0-rc2+ #9
[   88.378557] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
[   88.379504] Call Trace:
[   88.380019]  dump_stack+0x86/0xc7
[   88.380605]  __lock_acquire+0x841/0x1120
[   88.381252]  lock_acquire+0xd5/0x1c0
[   88.381865]  ? composite_disconnect+0x43/0x100 [libcomposite]
[   88.382668]  _raw_spin_lock_irqsave+0x40/0x54
[   88.383357]  ? composite_disconnect+0x43/0x100 [libcomposite]
[   88.384290]  composite_disconnect+0x43/0x100 [libcomposite]
[   88.385490]  set_link_state+0x2d4/0x3c0 [dummy_hcd]
[   88.386436]  dummy_pullup+0xa7/0xf0 [dummy_hcd]
[   88.387195]  usb_gadget_disconnect+0xd8/0x160 [udc_core]
[   88.387990]  usb_gadget_deactivate+0xd3/0x160 [udc_core]
[   88.388793]  usb_function_deactivate+0x64/0x80 [libcomposite]
[   88.389628]  uvc_function_disconnect+0x1e/0x40 [usb_f_uvc]

This patch changes the code to test the port-power status bit rather
than the port-connect status bit when deciding whether to isue the
callback.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: David Tulloh <david@tulloh.id.au>
CC: <stable@vger.kernel.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

Author: AlanStern

drivers/usb/gadget/udc/dummy_hcd.c

@@ -419,6 +419,7 @@ static void set_link_state_by_speed(struct dummy_hcd *dum_hcd)
 static void set_link_state(struct dummy_hcd *dum_hcd)
 {
 	struct dummy *dum = dum_hcd->dum;
+	unsigned int power_bit;
 
 	dum_hcd->active = 0;
 	if (dum->pullup)
@@ -429,17 +430,19 @@ static void set_link_state(struct dummy_hcd *dum_hcd)
 			return;
 
 	set_link_state_by_speed(dum_hcd);
+	power_bit = (dummy_hcd_to_hcd(dum_hcd)->speed == HCD_USB3 ?
+			USB_SS_PORT_STAT_POWER : USB_PORT_STAT_POWER);
 
 	if ((dum_hcd->port_status & USB_PORT_STAT_ENABLE) == 0 ||
 	     dum_hcd->active)
 		dum_hcd->resuming = 0;
 
 	/* Currently !connected or in reset */
-	if ((dum_hcd->port_status & USB_PORT_STAT_CONNECTION) == 0 ||
+	if ((dum_hcd->port_status & power_bit) == 0 ||
 			(dum_hcd->port_status & USB_PORT_STAT_RESET) != 0) {
-		unsigned disconnect = USB_PORT_STAT_CONNECTION &
+		unsigned int disconnect = power_bit &
 				dum_hcd->old_status & (~dum_hcd->port_status);
-		unsigned reset = USB_PORT_STAT_RESET &
+		unsigned int reset = USB_PORT_STAT_RESET &
 				(~dum_hcd->old_status) & dum_hcd->port_status;
 
 		/* Report reset and disconnect events to the driver */