[PATCH] wimax/i2400m: fix erroneous NETDEV_TX_BUSY use

Eric Dumazet
2012-03-14T19:21:46Z

A driver start_xmit() method cannot free skb and return NETDEV_TX_BUSY,
since caller is going to reuse freed skb.

In fact netif_tx_stop_queue() / netif_stop_queue() is needed before
returning NETDEV_TX_BUSY or you can trigger a ksoftirqd fatal loop.

In case of memory allocation error, only safe way is to drop the packet
and return NETDEV_TX_OK

Also increments tx_dropped counter

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
---
drivers/net/wimax/i2400m/netdev.c | 30 +++++++++-------------------
1 file changed, 10 insertions(+), 20 deletions(-)

diff --git a/drivers/net/wimax/i2400m/netdev.c
b/drivers/net/wimax/i2400m/netdev.c
index 64a1106..63e4b70 100644
--- a/drivers/net/wimax/i2400m/netdev.c
+++ b/drivers/net/wimax/i2400m/netdev.c
@@ -367,38 +367,28 @@ netdev_tx_t i2400m_hard_start_xmit(struct sk_buff
*skb,
{
struct i2400m *i2400m = net_dev_to_i2400m(net_dev);
struct device *dev = i2400m_dev(i2400m);
- int result;
+ int result = -1;

d_fnstart(3, dev, "(skb %p net_dev %p)\n", skb, net_dev);
- if (skb_header_cloned(skb)) {
- /*
- * Make tcpdump/wireshark happy -- if they are
- * running, the skb is cloned and we will overwrite
- * the mac fields in i2400m_tx_prep_header. Expand
- * seems to fix this...
- */
- result = pskb_expand_head(skb, 0, 0, GFP_ATOMIC);
- if (result) {
- result = NETDEV_TX_BUSY;
- goto error_expand;
- }
- }
+
+ if (skb_header_cloned(skb) &&
+ pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
+ goto drop;

if (i2400m->state == I2400M_SS_IDLE)
result = i2400m_net_wake_tx(i2400m, net_dev, skb);
else
result = i2400m_net_tx(i2400m, net_dev, skb);
- if (result < 0)
+ if (result < 0) {
+drop:
net_dev->stats.tx_dropped++;
- else {
+ } else {
net_dev->stats.tx_packets++;
net_dev->stats.tx_bytes += skb->len;
}
- result = NETDEV_TX_OK;
-error_expand:
- kfree_skb(skb);
+ dev_kfree_skb(skb);
d_fnend(3, dev, "(skb %p net_dev %p) = %d\n", skb, net_dev, result);
- return result;
+ return NETDEV_TX_OK;
}