The netdev queue is stopped in tun_net_xmit after inserting an SKB into
the ring buffer if the ring buffer became full because of that. If the
insertion into the ptr_ring fails, the netdev queue is also stopped and
the SKB is dropped. However, this never happened in my testing. To ensure
that the ptr_ring change is available to the consumer before the netdev
queue stop, an smp_wmb() is used.
Then in tun_ring_recv, the new helper wake_netdev_queue is called in the
blocking wait queue and after consuming an SKB from the ptr_ring. This
helper first checks if the netdev queue has stopped. Then with the paired
smp_rmb() it is known that tun_net_xmit will not produce SKBs anymore.
With that knowledge, the helper can then wake the netdev queue if there is
at least a single spare slot in the ptr_ring by calling ptr_ring_spare
with cnt=1.
Co-developed-by: Tim Gebauer <tim.geba...@tu-dortmund.de>
Signed-off-by: Tim Gebauer <tim.geba...@tu-dortmund.de>
Signed-off-by: Simon Schippers <simon.schipp...@tu-dortmund.de>
---
drivers/net/tun.c | 33 ++++++++++++++++++++++++++++++---
1 file changed, 30 insertions(+), 3 deletions(-)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index cc6c50180663..735498e221d8 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1060,13 +1060,21 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb,
struct net_device *dev)
nf_reset_ct(skb);
- if (ptr_ring_produce(&tfile->tx_ring, skb)) {
+ queue = netdev_get_tx_queue(dev, txq);
+ if (unlikely(ptr_ring_produce(&tfile->tx_ring, skb))) {
+ /* Paired with smp_rmb() in wake_netdev_queue. */
+ smp_wmb();
+ netif_tx_stop_queue(queue);
drop_reason = SKB_DROP_REASON_FULL_RING;
goto drop;
}
+ if (ptr_ring_full(&tfile->tx_ring)) {
+ /* Paired with smp_rmb() in wake_netdev_queue. */
+ smp_wmb();
+ netif_tx_stop_queue(queue);
+ }
/* dev->lltx requires to do our own update of trans_start */
- queue = netdev_get_tx_queue(dev, txq);
txq_trans_cond_update(queue);
/* Notify and wake up reader process */
@@ -2110,6 +2118,24 @@ static ssize_t tun_put_user(struct tun_struct *tun,
return total;
}
+static inline void wake_netdev_queue(struct tun_file *tfile)
+{
+ struct netdev_queue *txq;
+ struct net_device *dev;
+
+ rcu_read_lock();
+ dev = rcu_dereference(tfile->tun)->dev;
+ txq = netdev_get_tx_queue(dev, tfile->queue_index);
+
+ if (netif_tx_queue_stopped(txq)) {
+ /* Paired with smp_wmb() in tun_net_xmit. */
+ smp_rmb();
+ if (ptr_ring_spare(&tfile->tx_ring, 1))
+ netif_tx_wake_queue(txq);
+ }
+ rcu_read_unlock();
+}
+
static void *tun_ring_recv(struct tun_file *tfile, int noblock, int *err)
{
DECLARE_WAITQUEUE(wait, current);
@@ -2139,7 +2165,7 @@ static void *tun_ring_recv(struct tun_file *tfile, int
noblock, int *err)
error = -EFAULT;
break;
}
-
+ wake_netdev_queue(tfile);
schedule();
}
@@ -2147,6 +2173,7 @@ static void *tun_ring_recv(struct tun_file *tfile, int
noblock, int *err)
remove_wait_queue(&tfile->socket.wq.wait, &wait);
out:
+ wake_netdev_queue(tfile);
*err = error;
return ptr;
}
--
2.43.0
