From 5395353e0c8272fe73ac914acd7e4add0da2bef0 Mon Sep 17 00:00:00 2001 From: Benedikt Spranger Date: Tue, 2 Oct 2007 14:40:48 -0700 Subject: [PATCH] usb-gadget-ether: prevent oops caused by error interrupt race Fix a longstanding race in the Ethernet gadget driver, which can cause an oops on device disconnect. The fix is just to make the TX path check whether its freelist is empty. That check is otherwise not necessary, since the queue is always stopped when that list empties (and restarted when request completion puts an entry back on that freelist). The race window starts when the network code decides to transmit a packet, and ends when hard_start_xmit() grabs the freelist lock. When disconnect() is called inside that window, it shuts down the TX queue and breaks the otherwise-solid assumption that packets are never sent through a TX queue that's stopped. Signed-off-by: Benedikt Spranger Signed-off-by: Thomas Gleixner Signed-off-by: David Brownell Signed-off-by: Andrew Morton Cc: stable Signed-off-by: Greg Kroah-Hartman --- drivers/usb/gadget/ether.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/drivers/usb/gadget/ether.c b/drivers/usb/gadget/ether.c index ff244f42723f..9f4fd7e849a0 100644 --- a/drivers/usb/gadget/ether.c +++ b/drivers/usb/gadget/ether.c @@ -1957,8 +1957,20 @@ static int eth_start_xmit (struct sk_buff *skb, struct net_device *net) } spin_lock_irqsave(&dev->req_lock, flags); + /* + * this freelist can be empty if an interrupt triggered disconnect() + * and reconfigured the gadget (shutting down this queue) after the + * network stack decided to xmit but before we got the spinlock. + */ + if (list_empty(&dev->tx_reqs)) { + spin_unlock_irqrestore(&dev->req_lock, flags); + return 1; + } + req = container_of (dev->tx_reqs.next, struct usb_request, list); list_del (&req->list); + + /* temporarily stop TX queue when the freelist empties */ if (list_empty (&dev->tx_reqs)) netif_stop_queue (net); spin_unlock_irqrestore(&dev->req_lock, flags); -- 2.20.1