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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>
This commit is contained in:
Dominic Curran 2014-01-22 03:03:23 +00:00 committed by David S. Miller
parent bdf4351bbc
commit fa35864e0b
1 changed files with 6 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
drivers/net/tun.c
View File

@ -738,15 +738,17 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
struct tun_struct *tun = netdev_priv(dev);
int txq = skb->queue_mapping;
struct tun_file *tfile;
u32 numqueues = 0;
rcu_read_lock();
tfile = rcu_dereference(tun->tfiles[txq]);
numqueues = ACCESS_ONCE(tun->numqueues);
/* Drop packet if interface is not attached */
if (txq >= tun->numqueues)
if (txq >= numqueues)
goto drop;
if (tun->numqueues == 1) {
if (numqueues == 1) {
/* Select queue was not called for the skbuff, so we extract the
* RPS hash and save it into the flow_table here.
*/
@ -779,8 +781,8 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
/* Limit the number of packets queued by dividing txq length with the
* number of queues.
*/
if (skb_queue_len(&tfile->socket.sk->sk_receive_queue)
>= dev->tx_queue_len / tun->numqueues)
if (skb_queue_len(&tfile->socket.sk->sk_receive_queue) * numqueues
>= dev->tx_queue_len)
goto drop;
if (unlikely(skb_orphan_frags(skb, GFP_ATOMIC)))