[PATCH] usb: gadget: udc: renesas_usb3: Fix a race in usb3_start_pipen()

[Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>]

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.

Fixes: 746bfe63bba3 ("usb: gadget: renesas_usb3: add support for Renesas USB3.0 peripheral controller")
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
---
 drivers/usb/gadget/udc/renesas_usb3.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/udc/renesas_usb3.c b/drivers/usb/gadget/udc/renesas_usb3.c
index 0c418ce50ba0..f1b35a39d1ba 100644
--- a/drivers/usb/gadget/udc/renesas_usb3.c
+++ b/drivers/usb/gadget/udc/renesas_usb3.c
@@ -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)
-- 
2.25.1