diff options
author | Eugene Shatokhin <eugene.shatokhin@rosalab.ru> | 2015-09-01 17:05:33 +0300 |
---|---|---|
committer | David S. Miller <davem@davemloft.net> | 2015-09-08 23:17:43 +0300 |
commit | fcb0bb6aab256288a4e0a8650d26e4096ec30319 (patch) | |
tree | 7bae541ff96089cca6609db0ae69c582a8e86a66 /drivers | |
parent | 46cdc9be0841b30ba612aec1878cb746faf280a4 (diff) | |
download | linux-fcb0bb6aab256288a4e0a8650d26e4096ec30319.tar.xz |
usbnet: Fix a race between usbnet_stop() and the BH
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.shatokhin@rosalab.ru>
Reviewed-by: Bjørn Mork <bjorn@mork.no>
Acked-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'drivers')
-rw-r--r-- | drivers/net/usb/usbnet.c | 39 |
1 files changed, 28 insertions, 11 deletions
diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c index e0498571ae26..b4cf10781348 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); } |