tun: handle ubuf refcount correctly when meet errors

We trigger uarg->callback() immediately after we decide do datacopy
even if caller want to do zerocopy. This will cause the callback
(vhost_net_zerocopy_callback) decrease the refcount. But when we meet
an error afterwards, the error handling in vhost handle_tx() will try
to decrease it again. This is wrong and fix this by delay the
uarg->callback() until we're sure there's no errors.

Reported-by: wangyunjian <wangyunjian@huawei.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 6 deletions

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 8093e39ae263..db6acecabeaa 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1246,13 +1246,8 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 
         if (zerocopy)
                 err = zerocopy_sg_from_iter(skb, from);
-        else {
+        else
                 err = skb_copy_datagram_from_iter(skb, 0, from, len);
-                if (!err && msg_control) {
-                        struct ubuf_info *uarg = msg_control;
-                        uarg->callback(uarg, false);
-                }
-        }
 
         if (err) {
                 this_cpu_inc(tun->pcpu_stats->rx_dropped);
@@ -1298,6 +1293,9 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
                 skb_shinfo(skb)->destructor_arg = msg_control;
                 skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
                 skb_shinfo(skb)->tx_flags |= SKBTX_SHARED_FRAG;
+        } else if (msg_control) {
+                struct ubuf_info *uarg = msg_control;
+                uarg->callback(uarg, false);
         }
 
         skb_reset_network_header(skb);