2.6.27-stable review patch. If anyone has any objections, please let us know. ------------------ From: David Brownell commit e50ae572b33646656fa7037541613834dcadedfb upstream. This fixes a deadlock appearing with some USB peripheral drivers when running CDC ACM gadget code. The newish (2.6.27) CDC ACM event notification mechanism sends messages (IN to the host) which are short enough to fit in most FIFOs. That means that with some peripheral controller drivers (evidently not the ones used to verify the notification code!!) the completion callback can be issued before queue() returns. The deadlock would come because the completion callback and the event-issuing code shared a spinlock. Fix is trivial: drop that lock while queueing the message. Signed-off-by: David Brownell Signed-off-by: Greg Kroah-Hartman --- drivers/usb/gadget/f_acm.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/drivers/usb/gadget/f_acm.c +++ b/drivers/usb/gadget/f_acm.c @@ -463,7 +463,11 @@ static int acm_cdc_notify(struct f_acm * notify->wLength = cpu_to_le16(length); memcpy(buf, data, length); + /* ep_queue() can complete immediately if it fills the fifo... */ + spin_unlock(&acm->lock); status = usb_ep_queue(ep, req, GFP_ATOMIC); + spin_lock(&acm->lock); + if (status < 0) { ERROR(acm->port.func.config->cdev, "acm ttyGS%d can't notify serial state, %d\n", -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/