macvtap: zerocopy: set SKBTX_DEV_ZEROCOPY only when skb is built successfully

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@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 5 insertions, 4 deletions

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 9ab182a40648..a4ff694cea22 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -699,10 +699,9 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *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)
@@ -721,8 +720,10 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *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