FAILED: patch "[PATCH] usb: gadget: udc: renesas_usb3: Fix a race in" failed to apply to 4.9-stable tree

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From e752dbc59e1241b13b8c4f7b6eb582862e7668fe Mon Sep 17 00:00:00 2001
From: Yoshihiro Shimoda <[email protected]>
Date: Mon, 24 May 2021 15:01:55 +0900
Subject: [PATCH] usb: gadget: udc: renesas_usb3: Fix a race in
usb3_start_pipen()

The usb3_start_pipen() is called by renesas_usb3_ep_queue() and usb3_request_done_pipen() so that usb3_start_pipen() is possible to cause a race when getting usb3_first_req like below:

renesas_usb3_ep_queue()
spin_lock_irqsave()
list_add_tail()
spin_unlock_irqrestore()
usb3_start_pipen()
usb3_first_req = usb3_get_request() --- [1]
--- interrupt ---
usb3_irq_dma_int()
usb3_request_done_pipen()
usb3_get_request()
usb3_start_pipen()
usb3_first_req = usb3_get_request()
...
(the req is possible to be finished in the interrupt)

The usb3_first_req [1] above may have been finished after the interrupt ended so that this driver caused to start a transfer wrongly. To fix this issue, getting/checking the usb3_first_req are under spin_lock_irqsave() in the same section.

index 0c418ce50ba0..f1b35a39d1ba 100644
@@ -1488,7 +1488,7 @@ static void usb3_start_pipen(struct renesas_usb3_ep *usb3_ep,
 			     struct renesas_usb3_request *usb3_req)
 {
 	struct renesas_usb3 *usb3 = usb3_ep_to_usb3(usb3_ep);
-	struct renesas_usb3_request *usb3_req_first = usb3_get_request(usb3_ep);
+	struct renesas_usb3_request *usb3_req_first;
 	unsigned long flags;
 	int ret = -EAGAIN;
 	u32 enable_bits = 0;

@@ -1496,7 +1496,8 @@ static void usb3_start_pipen(struct renesas_usb3_ep *usb3_ep,
 	spin_lock_irqsave(&usb3->lock, flags);
 	if (usb3_ep->halt || usb3_ep->started)
 		goto out;
-	if (usb3_req != usb3_req_first)
+	usb3_req_first = __usb3_get_request(usb3_ep);
+	if (!usb3_req_first || usb3_req != usb3_req_first)
 		goto out;
 
 	if (usb3_pn_change(usb3, usb3_ep->num) < 0)