[PATCH v3] usb: dwc3: gadget: Replace list_for_each_entry_safe() if using giveback

[Wesley Cheng <quic_wcheng@quicinc.com>]

The list_for_each_entry_safe() macro saves the current item (n) and
the item after (n+1), so that n can be safely removed without
corrupting the list.  However, when traversing the list and removing
items using gadget giveback, the DWC3 lock is briefly released,
allowing other routines to execute.  There is a situation where, while
items are being removed from the cancelled_list using
dwc3_gadget_ep_cleanup_cancelled_requests(), the pullup disable
routine is running in parallel (due to UDC unbind).  As the cleanup
routine removes n, and the pullup disable removes n+1, once the
cleanup retakes the DWC3 lock, it references a request who was already
removed/handled.  With list debug enabled, this leads to a panic.
Ensure all instances of the macro are replaced where gadget giveback
is used.

Example call stack:

Thread#1:
__dwc3_gadget_ep_set_halt() - CLEAR HALT
  -> dwc3_gadget_ep_cleanup_cancelled_requests()
    ->list_for_each_entry_safe()
    ->dwc3_gadget_giveback(n)
      ->dwc3_gadget_del_and_unmap_request()- n deleted[cancelled_list]
      ->spin_unlock
      ->Thread#2 executes
      ...
    ->dwc3_gadget_giveback(n+1)
      ->Already removed!

Thread#2:
dwc3_gadget_pullup()
  ->waiting for dwc3 spin_lock
  ...
  ->Thread#1 released lock
  ->dwc3_stop_active_transfers()
    ->dwc3_remove_requests()
      ->fetches n+1 item from cancelled_list (n removed by Thread#1)
      ->dwc3_gadget_giveback()
        ->dwc3_gadget_del_and_unmap_request()- n+1 deleted[cancelled_list]
        ->spin_unlock

Fixes: d4f1afe5e896 ("usb: dwc3: gadget: move requests to cancelled_list")
Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
---
Changes in v3:
 - Added endpoint disable check while looping

Changes in v2:
 - Updated commit message with context call stack of an example scenario
   seen on device

 drivers/usb/dwc3/gadget.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index ce1b130202c5..10271ac9594d 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -2001,10 +2001,10 @@ static void dwc3_gadget_ep_skip_trbs(struct dwc3_ep *dep, struct dwc3_request *r
 static void dwc3_gadget_ep_cleanup_cancelled_requests(struct dwc3_ep *dep)
 {
 	struct dwc3_request		*req;
-	struct dwc3_request		*tmp;
 	struct dwc3			*dwc = dep->dwc;
 
-	list_for_each_entry_safe(req, tmp, &dep->cancelled_list, list) {
+	while (!list_empty(&dep->cancelled_list)) {
+		req = next_request(&dep->cancelled_list);
 		dwc3_gadget_ep_skip_trbs(dep, req);
 		switch (req->status) {
 		case DWC3_REQUEST_STATUS_DISCONNECTED:
@@ -2021,6 +2021,12 @@ static void dwc3_gadget_ep_cleanup_cancelled_requests(struct dwc3_ep *dep)
 			dwc3_gadget_giveback(dep, req, -ECONNRESET);
 			break;
 		}
+		/*
+		 * The endpoint is disabled, let the dwc3_remove_requests()
+		 * handle the cleanup.
+		 */
+		if (!dep->endpoint.desc)
+			break;
 	}
 }
 
@@ -3307,15 +3313,21 @@ static void dwc3_gadget_ep_cleanup_completed_requests(struct dwc3_ep *dep,
 		const struct dwc3_event_depevt *event, int status)
 {
 	struct dwc3_request	*req;
-	struct dwc3_request	*tmp;
 
-	list_for_each_entry_safe(req, tmp, &dep->started_list, list) {
+	while (!list_empty(&dep->started_list)) {
 		int ret;
 
+		req = next_request(&dep->started_list);
 		ret = dwc3_gadget_ep_cleanup_completed_request(dep, event,
 				req, status);
 		if (ret)
 			break;
+		/*
+		 * The endpoint is disabled, let the dwc3_remove_requests()
+		 * handle the cleanup.
+		 */
+		if (!dep->endpoint.desc)
+			break;
 	}
 }