[ 170/218] macvtap: zerocopy: set SKBTX_DEV_ZEROCOPY only when skb is built successfully

From: Greg Kroah-Hartman
Date: Fri Sep 28 2012 - 16:30:35 EST


3.4-stable review patch. If anyone has any objections, please let me know.

------------------

From: Jason Wang <jasowang@xxxxxxxxxx>

commit 01d6657b388438def19c8baaea28e742b6ed32ec upstream.

Current the SKBTX_DEV_ZEROCOPY is set unconditionally after
zerocopy_sg_from_iovec(), this would lead NULL pointer when macvtap
fails to build zerocopy skb because destructor_arg was not
initialized. Solve this by set this flag after the skb were built
successfully.

Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Cc: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
drivers/net/macvtap.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -716,10 +716,9 @@ static ssize_t macvtap_get_user(struct m
if (!skb)
goto err;

- if (zerocopy) {
+ if (zerocopy)
err = zerocopy_sg_from_iovec(skb, iv, vnet_hdr_len, count);
- skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
- } else
+ else
err = skb_copy_datagram_from_iovec(skb, 0, iv, vnet_hdr_len,
len);
if (err)
@@ -738,8 +737,10 @@ static ssize_t macvtap_get_user(struct m
rcu_read_lock_bh();
vlan = rcu_dereference_bh(q->vlan);
/* copy skb_ubuf_info for callback when skb has no error */
- if (zerocopy)
+ if (zerocopy) {
skb_shinfo(skb)->destructor_arg = m->msg_control;
+ skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
+ }
if (vlan)
macvlan_start_xmit(skb, vlan->dev);
else


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