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authorDominic Curran <dominic.curran@citrix.com>2014-01-21 22:03:23 -0500
committerDavid S. Miller <davem@davemloft.net>2014-01-23 00:32:56 -0500
commitfa35864e0bb7f7c13b9c6d6751ddac9b42d4810f (patch)
tree50f705ece98607b7a54161554b486d65c426ac2e
parentbdf4351bbc62f3b24151cf19ca6e531b68d8c340 (diff)
tuntap: Fix for a race in accessing numqueues
A patch for fixing a race between queue selection and changing queues was introduced in commit 92bb73ea2("tuntap: fix a possible race between queue selection and changing queues"). The fix was to prevent the driver from re-reading the tun->numqueues more than once within tun_select_queue() using ACCESS_ONCE(). We have been experiancing 'Divide-by-zero' errors in tun_net_xmit() since we moved from 3.6 to 3.10, and believe that they come from a simular source where the value of tun->numqueues changes to zero between the first and a subsequent read of tun->numqueues. The fix is a simular use of ACCESS_ONCE(), as well as a multiply instead of a divide in the if statement. Signed-off-by: Dominic Curran <dominic.curran@citrix.com> Cc: Jason Wang <jasowang@redhat.com> Cc: Maxim Krasnyansky <maxk@qti.qualcomm.com> Acked-by: Jason Wang <jasowang@redhat.com> Acked-by: Max Krasnyansky <maxk@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--drivers/net/tun.c10
1 files changed, 6 insertions, 4 deletions
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 34cca74c99ed..bcf01af4b879 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -738,15 +738,17 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
738 struct tun_struct *tun = netdev_priv(dev); 738 struct tun_struct *tun = netdev_priv(dev);
739 int txq = skb->queue_mapping; 739 int txq = skb->queue_mapping;
740 struct tun_file *tfile; 740 struct tun_file *tfile;
741 u32 numqueues = 0;
741 742
742 rcu_read_lock(); 743 rcu_read_lock();
743 tfile = rcu_dereference(tun->tfiles[txq]); 744 tfile = rcu_dereference(tun->tfiles[txq]);
745 numqueues = ACCESS_ONCE(tun->numqueues);
744 746
745 /* Drop packet if interface is not attached */ 747 /* Drop packet if interface is not attached */
746 if (txq >= tun->numqueues) 748 if (txq >= numqueues)
747 goto drop; 749 goto drop;
748 750
749 if (tun->numqueues == 1) { 751 if (numqueues == 1) {
750 /* Select queue was not called for the skbuff, so we extract the 752 /* Select queue was not called for the skbuff, so we extract the
751 * RPS hash and save it into the flow_table here. 753 * RPS hash and save it into the flow_table here.
752 */ 754 */
@@ -779,8 +781,8 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
779 /* Limit the number of packets queued by dividing txq length with the 781 /* Limit the number of packets queued by dividing txq length with the
780 * number of queues. 782 * number of queues.
781 */ 783 */
782 if (skb_queue_len(&tfile->socket.sk->sk_receive_queue) 784 if (skb_queue_len(&tfile->socket.sk->sk_receive_queue) * numqueues
783 >= dev->tx_queue_len / tun->numqueues) 785 >= dev->tx_queue_len)
784 goto drop; 786 goto drop;
785 787
786 if (unlikely(skb_orphan_frags(skb, GFP_ATOMIC))) 788 if (unlikely(skb_orphan_frags(skb, GFP_ATOMIC)))