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>

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 9ab182a4064800e2c39e99426fb3a83872bb8a2d..a4ff694cea228c4d98289c5ab3dde2f7d430005b 100644 (file)
--- 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