01.09.2015 17:05, Eugene Shatokhin пишет:
The race may happen when a device (e.g. YOTA 4G LTE Modem) is unplugged while the system is downloading a large file from the Net.Hardware breakpoints and Kprobes with delays were used to confirm that the race does actually happen. The race is on skb_queue ('next' pointer) between usbnet_stop() and rx_complete(), which, in turn, calls usbnet_bh(). Here is a part of the call stack with the code where the changes to the queue happen. The line numbers are for the kernel 4.1.0: *0 __skb_unlink (skbuff.h:1517) prev->next = next; *1 defer_bh (usbnet.c:430) spin_lock_irqsave(&list->lock, flags); old_state = entry->state; entry->state = state; __skb_unlink(skb, list); spin_unlock(&list->lock); spin_lock(&dev->done.lock); __skb_queue_tail(&dev->done, skb); if (dev->done.qlen == 1) tasklet_schedule(&dev->bh); spin_unlock_irqrestore(&dev->done.lock, flags); *2 rx_complete (usbnet.c:640) state = defer_bh(dev, skb, &dev->rxq, state); At the same time, the following code repeatedly checks if the queue is empty and reads these values concurrently with the above changes: *0 usbnet_terminate_urbs (usbnet.c:765) /* maybe wait for deletions to finish. */ while (!skb_queue_empty(&dev->rxq) && !skb_queue_empty(&dev->txq) && !skb_queue_empty(&dev->done)) { schedule_timeout(msecs_to_jiffies(UNLINK_TIMEOUT_MS)); set_current_state(TASK_UNINTERRUPTIBLE); netif_dbg(dev, ifdown, dev->net, "waited for %d urb completions\n", temp); } *1 usbnet_stop (usbnet.c:806) if (!(info->flags & FLAG_AVOID_UNLINK_URBS)) usbnet_terminate_urbs(dev); As a result, it is possible, for example, that the skb is removed from dev->rxq by __skb_unlink() before the check "!skb_queue_empty(&dev->rxq)" in usbnet_terminate_urbs() is made. It is also possible in this case that the skb is added to dev->done queue after "!skb_queue_empty(&dev->done)" is checked. So usbnet_terminate_urbs() may stop waiting and return while dev->done queue still has an item. Locking in defer_bh() and usbnet_terminate_urbs() was revisited to avoid this race. Signed-off-by: Eugene Shatokhin <eugene.shatok...@rosalab.ru> --- drivers/net/usb/usbnet.c | 39 ++++++++++++++++++++++++++++----------- 1 file changed, 28 insertions(+), 11 deletions(-) diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c index e049857..b4cf107 100644 --- a/drivers/net/usb/usbnet.c +++ b/drivers/net/usb/usbnet.c @@ -428,12 +428,18 @@ static enum skb_state defer_bh(struct usbnet *dev, struct sk_buff *skb, old_state = entry->state; entry->state = state; __skb_unlink(skb, list); - spin_unlock(&list->lock); - spin_lock(&dev->done.lock); + + /* defer_bh() is never called with list == &dev->done. + * spin_lock_nested() tells lockdep that it is OK to take + * dev->done.lock here with list->lock held. + */ + spin_lock_nested(&dev->done.lock, SINGLE_DEPTH_NESTING); + __skb_queue_tail(&dev->done, skb); if (dev->done.qlen == 1) tasklet_schedule(&dev->bh); - spin_unlock_irqrestore(&dev->done.lock, flags); + spin_unlock(&dev->done.lock); + spin_unlock_irqrestore(&list->lock, flags); return old_state; } @@ -749,6 +755,20 @@ EXPORT_SYMBOL_GPL(usbnet_unlink_rx_urbs); /*-------------------------------------------------------------------------*/ +static void wait_skb_queue_empty(struct sk_buff_head *q) +{ + unsigned long flags; + + spin_lock_irqsave(&q->lock, flags); + while (!skb_queue_empty(q)) { + spin_unlock_irqrestore(&q->lock, flags); + schedule_timeout(msecs_to_jiffies(UNLINK_TIMEOUT_MS)); + set_current_state(TASK_UNINTERRUPTIBLE); + spin_lock_irqsave(&q->lock, flags); + } + spin_unlock_irqrestore(&q->lock, flags); +} + // precondition: never called in_interrupt static void usbnet_terminate_urbs(struct usbnet *dev) { @@ -762,14 +782,11 @@ static void usbnet_terminate_urbs(struct usbnet *dev) unlink_urbs(dev, &dev->rxq); /* maybe wait for deletions to finish. */ - while (!skb_queue_empty(&dev->rxq) - && !skb_queue_empty(&dev->txq) - && !skb_queue_empty(&dev->done)) { - schedule_timeout(msecs_to_jiffies(UNLINK_TIMEOUT_MS)); - set_current_state(TASK_UNINTERRUPTIBLE); - netif_dbg(dev, ifdown, dev->net, - "waited for %d urb completions\n", temp); - } + wait_skb_queue_empty(&dev->rxq); + wait_skb_queue_empty(&dev->txq); + wait_skb_queue_empty(&dev->done); + netif_dbg(dev, ifdown, dev->net, + "waited for %d urb completions\n", temp); set_current_state(TASK_RUNNING); remove_wait_queue(&dev->wait, &wait); }
I resent the patch to make it separate. What is the status of this now? Regards, Eugene -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
