net/ixgbe: Fix concurrency issues between config flow and XSK

Use synchronize_rcu to wait until the XSK wakeup function finishes
before destroying the resources it uses:

1. ixgbe_down already calls synchronize_rcu after setting __IXGBE_DOWN.

2. After switching the XDP program, call synchronize_rcu to let
ixgbe_xsk_wakeup exit before the XDP program is freed.

3. Changing the number of channels brings the interface down.

4. Disabling UMEM sets __IXGBE_TX_DISABLED before closing hardware
resources and resetting xsk_umem. Check that bit in ixgbe_xsk_wakeup to
avoid using the XDP ring when it's already destroyed. synchronize_rcu is
called from ixgbe_txrx_ring_disable.
Signed-off-by: Maxim Mikityanskiy <maximmi@mellanox.com>
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20191217162023.16011-5-maximmi@mellanox.com

drivers/net/ethernet/intel/ixgbe/ixgbe_main.c

@@ -10261,7 +10261,12 @@ static int ixgbe_xdp_setup(struct net_device *dev, struct bpf_prog *prog)
 
 	/* If transitioning XDP modes reconfigure rings */
 	if (need_reset) {
-		int err = ixgbe_setup_tc(dev, adapter->hw_tcs);
+		int err;
+
+		if (!prog)
+			/* Wait until ndo_xsk_wakeup completes. */
+			synchronize_rcu();
+		err = ixgbe_setup_tc(dev, adapter->hw_tcs);
 
 		if (err) {
 			rcu_assign_pointer(adapter->xdp_prog, old_prog);

drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c

@@ -709,10 +709,14 @@ int ixgbe_xsk_wakeup(struct net_device *dev, u32 qid, u32 flags)
 	if (qid >= adapter->num_xdp_queues)
 		return -ENXIO;
 
-	if (!adapter->xdp_ring[qid]->xsk_umem)
+	ring = adapter->xdp_ring[qid];
+
+	if (test_bit(__IXGBE_TX_DISABLED, &ring->state))
+		return -ENETDOWN;
+
+	if (!ring->xsk_umem)
 		return -ENXIO;
 
-	ring = adapter->xdp_ring[qid];
 	if (!napi_if_scheduled_mark_missed(&ring->q_vector->napi)) {
 		u64 eics = BIT_ULL(ring->q_vector->v_idx);