[PATCH] usb: gadget: f_uac2: fixup feedback endpoint stop

[Jerome Brunet <jbrunet@baylibre.com>]

When the uac2 function is stopped, there seems to be an issue with some
platforms (Intel Merrifield at least)

BUG: kernel NULL pointer dereference, address: 0000000000000008
...
RIP: 0010:dwc3_gadget_del_and_unmap_request+0x19/0xe0
...
Call Trace:
 dwc3_remove_requests.constprop.0+0x12f/0x170
 __dwc3_gadget_ep_disable+0x7a/0x160
 dwc3_gadget_ep_disable+0x3d/0xd0
 usb_ep_disable+0x1c/0x70
 u_audio_stop_capture+0x79/0x120 [u_audio]
 afunc_set_alt+0x73/0x80 [usb_f_uac2]
 composite_setup+0x224/0x1b90 [libcomposite]

The issue happens only when the gadget is using the sync type "async", not
"adaptive". This indicates that problem is likely coming from the feedback
endpoint, which is only used with async synchronization mode.

Update the feedback endpoint free function to release the endpoint the same
way it is done for the data endpoint.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
---

 Hi Ferry,

 Would you mind trying this before reverting the whole thing ?
 The HW I have did not show the issue so far so I can't really check
 if it helps. Hopefully, it does ...

 drivers/usb/gadget/function/u_audio.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/gadget/function/u_audio.c b/drivers/usb/gadget/function/u_audio.c
index 018dd0978995..63d9340f008e 100644
--- a/drivers/usb/gadget/function/u_audio.c
+++ b/drivers/usb/gadget/function/u_audio.c
@@ -230,7 +230,13 @@ static void u_audio_iso_fback_complete(struct usb_ep *ep,
 	int status = req->status;
 
 	/* i/f shutting down */
-	if (!prm->fb_ep_enabled || req->status == -ESHUTDOWN)
+	if (!prm->fb_ep_enabled) {
+		kfree(req->buf);
+		usb_ep_free_request(ep, req);
+		return;
+	}
+
+	if (req->status == -ESHUTDOWN)
 		return;
 
 	/*
@@ -421,9 +427,10 @@ static inline void free_ep_fback(struct uac_rtd_params *prm, struct usb_ep *ep)
 	prm->fb_ep_enabled = false;
 
 	if (prm->req_fback) {
-		usb_ep_dequeue(ep, prm->req_fback);
-		kfree(prm->req_fback->buf);
-		usb_ep_free_request(ep, prm->req_fback);
+		if (usb_ep_dequeue(ep, prm->req_fback)) {
+			kfree(prm->req_fback->buf);
+			usb_ep_free_request(ep, prm->req_fback);
+		}
 		prm->req_fback = NULL;
 	}
 
-- 
2.33.0