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Date: Tue, 8 Sep 2015 10:24:09 +0300 From: Eugene Shatokhin <eugene.shatokhin@...alab.ru> To: Oliver Neukum <oneukum@...e.de>, Bjørn Mork <bjorn@...k.no>, David Miller <davem@...emloft.net> Cc: netdev@...r.kernel.org, linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] usbnet: Fix a race between usbnet_stop() and the BH 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.shatokhin@...alab.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 linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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