[PATCH 19/19] usb: dwc2: wait for the TT clear in endpoint_disable

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Josef Bacik <josef@toxicpanda.com>

When a split transaction fails, dwc2_hc_handle_tt_clear() sets
qh->tt_buffer_dirty and calls usb_hub_clear_tt_buffer(). The hub driver
stores urb->ep in its list and hub_tt_work() hands it back to
_dwc2_hcd_clear_tt_buffer_complete() after the CLEAR_TT_BUFFER request to
the hub, which can take up to a second if the hub does not answer.

Nothing keeps the endpoint until then. dwc2_hcd_endpoint_disable() only
waits for the QTD list to drain and frees the QH. If the full or low
speed device is unplugged, usb_disconnect() goes on to free the
usb_device and its configurations, which hold the struct
usb_host_endpoint. The callback then reads ep->hcpriv from freed memory
and, if it is not NULL, clears a bit in whatever it points to. A change
of the configuration or altsetting only frees the QH, under a callback
which has loaded ep->hcpriv without the lock.

A device which contains a hub can provoke this: fail a transaction of
the downstream device, report its disconnection and hold back the answer
to CLEAR_TT_BUFFER.

The HCD has to wait, like ehci_endpoint_disable(),
xhci_endpoint_disable() and fotg210_endpoint_disable() do. hub_tt_work()
calls the callback for every entry, also if the request failed, and
hub_quiesce() flushes the work, so the wait ends.

Fixes: 7359d482eb4d ("staging: HCD files for the DWC2 driver")
Cc: stable <stable@kernel.org>
Cc: Minas Harutyunyan <hminas@synopsys.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/usb/dwc2/hcd.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/usb/dwc2/hcd.c b/drivers/usb/dwc2/hcd.c
index d5275cd658d4..a6ee55c494f8 100644
--- a/drivers/usb/dwc2/hcd.c
+++ b/drivers/usb/dwc2/hcd.c
@@ -1993,6 +1993,21 @@ static int dwc2_hcd_endpoint_disable(struct dwc2_hsotg *hsotg,
 		}
 	}
 
+	/*
+	 * The hub driver still has a pointer to the endpoint. Wait until it
+	 * has called _dwc2_hcd_clear_tt_buffer_complete().
+	 */
+	while (qh->tt_buffer_dirty) {
+		spin_unlock_irqrestore(&hsotg->lock, flags);
+		msleep(20);
+		spin_lock_irqsave(&hsotg->lock, flags);
+		qh = ep->hcpriv;
+		if (!qh) {
+			rc = -EINVAL;
+			goto err;
+		}
+	}
+
 	dwc2_hcd_qh_unlink(hsotg, qh);
 
 	/* Free each QTD in the QH's QTD list */

-- 
2.56.0