[PATCH][RESEND] usb: dwc3: gadget: Handle dequeuing of non queued URB gracefully

[Alexandru Ardelean <alexandru.ardelean@analog.com>]

From: Lars-Peter Clausen <lars@metafoo.de>

Trying to dequeue and URB that is currently not queued should be a no-op
and be handled gracefully.

Use the list field of the URB to indicate whether it is queued or not by
setting it to the empty list when it is not queued.

Handling this gracefully allows for race condition free synchronization
between the complete callback being called to to a completed transfer and
trying to call usb_ep_dequeue() at the same time.

Tested-by: Michael Olbrich <m.olbrich@pengutronix.de>
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
---

* Added Michael Olbrich's Tested-by tag
  https://lore.kernel.org/linux-usb/20191112144108.GA1859@pengutronix.de/

 drivers/usb/dwc3/gadget.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 1b8014ab0b25..22a78eb41a5b 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -177,7 +177,7 @@ static void dwc3_gadget_del_and_unmap_request(struct dwc3_ep *dep,
 {
 	struct dwc3			*dwc = dep->dwc;
 
-	list_del(&req->list);
+	list_del_init(&req->list);
 	req->remaining = 0;
 	req->needs_extra_trb = false;
 
@@ -847,6 +847,7 @@ static struct usb_request *dwc3_gadget_ep_alloc_request(struct usb_ep *ep,
 	req->epnum	= dep->number;
 	req->dep	= dep;
 	req->status	= DWC3_REQUEST_STATUS_UNKNOWN;
+	INIT_LIST_HEAD(&req->list);
 
 	trace_dwc3_alloc_request(req);
 
@@ -1549,6 +1550,10 @@ static int dwc3_gadget_ep_dequeue(struct usb_ep *ep,
 
 	spin_lock_irqsave(&dwc->lock, flags);
 
+	/* Not queued, nothing to do */
+	if (list_empty(&req->list))
+		goto out0;
+
 	list_for_each_entry(r, &dep->pending_list, list) {
 		if (r == req)
 			break;
-- 
2.20.1