xhci: fix deadlock at host remove by running watchdog correctly

commit d6169d04 upstream.

If a URB is killed while the host is removed we can end up in a situation
where the hub thread takes the roothub device lock, and waits for
the URB to be given back by xhci-hcd, blocking the host remove code.

xhci-hcd tries to stop the endpoint and give back the urb, but can't
as the host is removed from PCI bus at the same time, preventing the normal
way of giving back urb.

Instead we need to rely on the stop command timeout function to give back
the urb. This xhci_stop_endpoint_command_watchdog() timeout function
used a XHCI_STATE_DYING flag to indicate if the timeout function is already
running, but later this flag has been taking into use in other places to
mark that xhci is dying.

Remove checks for XHCI_STATE_DYING in xhci_urb_dequeue. We are still
checking that reading from pci state does not return 0xffffffff or that
host is not halted before trying to stop the endpoint.

This whole area of stopping endpoints, giving back URBs, and the wathdog
timeout need rework, this fix focuses on solving a specific deadlock
issue that we can then send to stable before any major rework.
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.16: the checks look slightly different]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/usb/host/xhci-ring.c

@@ -878,13 +878,6 @@ void xhci_stop_endpoint_command_watchdog(unsigned long arg)
 	spin_lock_irqsave(&xhci->lock, flags);
 
 	ep->stop_cmds_pending--;
-	if (xhci->xhc_state & XHCI_STATE_DYING) {
-		xhci_dbg_trace(xhci, trace_xhci_dbg_cancel_urb,
-				"Stop EP timer ran, but another timer marked "
-				"xHCI as DYING, exiting.");
-		spin_unlock_irqrestore(&xhci->lock, flags);
-		return;
-	}
 	if (!(ep->stop_cmds_pending == 0 && (ep->ep_state & EP_HALT_PENDING))) {
 		xhci_dbg_trace(xhci, trace_xhci_dbg_cancel_urb,
 				"Stop EP timer ran, but no command pending, "

drivers/usb/host/xhci.c

@@ -1561,19 +1561,6 @@ int xhci_urb_dequeue(struct usb_hcd *hcd, struct urb *urb, int status)
 		xhci_urb_free_priv(xhci, urb_priv);
 		return ret;
 	}
-	if ((xhci->xhc_state & XHCI_STATE_DYING) ||
-			(xhci->xhc_state & XHCI_STATE_HALTED)) {
-		xhci_dbg_trace(xhci, trace_xhci_dbg_cancel_urb,
-				"Ep 0x%x: URB %p to be canceled on "
-				"non-responsive xHCI host.",
-				urb->ep->desc.bEndpointAddress, urb);
-		/* Let the stop endpoint command watchdog timer (which set this
-		 * state) finish cleaning up the endpoint TD lists.  We must
-		 * have caught it in the middle of dropping a lock and giving
-		 * back an URB.
-		 */
-		goto done;
-	}
 
 	ep_index = xhci_get_endpoint_index(&urb->ep->desc);
 	ep = &xhci->devs[urb->dev->slot_id]->eps[ep_index];