From akpm@linux-foundation.org Tue Oct 2 14:40:55 2007 From: Benedikt Spranger Date: Tue, 02 Oct 2007 14:40:48 -0700 Subject: usb-gadget-ether: prevent oops caused by error interrupt race To: greg@kroah.com Cc: linux-usb-devel@lists.sourceforge.net, akpm@linux-foundation.org, bene@linutronix.de, dbrownell@users.sourceforge.net, tglx@linutronix.de Message-ID: <200710022140.l92LemTT023767@imap1.linux-foundation.org> From: Benedikt Spranger 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(+) --- a/drivers/usb/gadget/ether.c +++ b/drivers/usb/gadget/ether.c @@ -1957,8 +1957,20 @@ static int eth_start_xmit (struct sk_buf } 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);