usb: dwc2: gadget: Fix kill_all_requests race

When a gadget is disabled, kill_all_requests() can be called
simultaneously from both a user process via dwc2_hsotg_pullup() and from
the interrupt handler if the hardware detects disconnection.

Since we drop the lock in dwc2_hsotg_complete_request() in order to call
the completion handler, this means that the list is modified
concurrently and leads to an infinite loop in kill_all_requests().

Replace the foreach loop with a while-not-empty loop in order to remove
the danger of this concurrent modification.

Note: I observed this with threadirqs, I'm not sure if it can be
triggered without threaded interrupts.
Signed-off-by: John Keeping <john@metanate.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc2/gadget.c

@@ -3224,14 +3224,15 @@ static void kill_all_requests(struct dwc2_hsotg *hsotg,
 			      struct dwc2_hsotg_ep *ep,
 			      int result)
 {
-	struct dwc2_hsotg_req *req, *treq;
 	unsigned int size;
 
 	ep->req = NULL;
 
-	list_for_each_entry_safe(req, treq, &ep->queue, queue)
-		dwc2_hsotg_complete_request(hsotg, ep, req,
-					    result);
+	while (!list_empty(&ep->queue)) {
+		struct dwc2_hsotg_req *req = get_ep_head(ep);
+
+		dwc2_hsotg_complete_request(hsotg, ep, req, result);
+	}
 
 	if (!hsotg->dedicated_fifos)
 		return;