usb: renesas_usbhs: fix to avoid using a disabled ep in usbhsg_queue_done()

This patch fixes an issue that usbhsg_queue_done() may cause kernel
panic when dma callback is running and usb_ep_disable() is called
by interrupt handler. (Especially, we can reproduce this issue using
g_audio with usb-dmac driver.)

For example of a flow:
 usbhsf_dma_complete (on tasklet)
  --> usbhsf_pkt_handler (on tasklet)
   --> usbhsg_queue_done (on tasklet)
    *** interrupt happened and usb_ep_disable() is called ***
    --> usbhsg_queue_pop (on tasklet)
     Then, oops happened.

Fixes: e73a9891 ("usb: renesas_usbhs: add DMAEngine support")
Cc: <stable@vger.kernel.org> # v3.1+
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/renesas_usbhs/mod_gadget.c

@@ -158,10 +158,14 @@ static void usbhsg_queue_done(struct usbhs_priv *priv, struct usbhs_pkt *pkt)
 	struct usbhs_pipe *pipe = pkt->pipe;
 	struct usbhsg_uep *uep = usbhsg_pipe_to_uep(pipe);
 	struct usbhsg_request *ureq = usbhsg_pkt_to_ureq(pkt);
+	unsigned long flags;
 
 	ureq->req.actual = pkt->actual;
 
-	usbhsg_queue_pop(uep, ureq, 0);
+	usbhs_lock(priv, flags);
+	if (uep)
+		__usbhsg_queue_pop(uep, ureq, 0);
+	usbhs_unlock(priv, flags);
 }
 
 static void usbhsg_queue_push(struct usbhsg_uep *uep,