net/ipv4: Use non-atomic allocation of udp offloads structure instance

Since udp_add_offload() can be called from non-sleepable context e.g
under this call tree from the vxlan driver use case:

  vxlan_socket_create() <-- holds the spinlock
  -> vxlan_notify_add_rx_port()
     -> udp_add_offload()  <-- schedules

we should allocate the udp_offloads structure in atomic manner.

Fixes: b582ef09 ('net: Add GRO support for UDP encapsulating protocols')
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NOr Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/udp_offload.c

@@ -101,7 +101,7 @@ static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
 int udp_add_offload(struct udp_offload *uo)
 {
 	struct udp_offload_priv __rcu **head = &udp_offload_base;
-	struct udp_offload_priv *new_offload = kzalloc(sizeof(*new_offload), GFP_KERNEL);
+	struct udp_offload_priv *new_offload = kzalloc(sizeof(*new_offload), GFP_ATOMIC);
 
 	if (!new_offload)
 		return -ENOMEM;