ice: synchronize_rcu() when terminating rings

Unfortunately, the ice driver doesn't respect the RCU critical section that
XSK wakeup is surrounded with. To fix this, add synchronize_rcu() calls to
paths that destroy resources that might be in use.

This was addressed in other AF_XDP ZC enabled drivers, for reference see
for example commit b3873a5 ("net/i40e: Fix concurrency issues
between config flow and XSK")

Fixes: efc2214 ("ice: Add support for XDP")
Fixes: 2d4238f ("ice: Add support for AF_XDP")
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Tested-by: Shwetha Nagaraju <shwetha.nagaraju@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

Author: mfijalko

drivers/net/ethernet/intel/ice/ice.h

@@ -671,7 +671,7 @@ static inline struct ice_pf *ice_netdev_to_pf(struct net_device *netdev)
 
 static inline bool ice_is_xdp_ena_vsi(struct ice_vsi *vsi)
 {
-	return !!vsi->xdp_prog;
+	return !!READ_ONCE(vsi->xdp_prog);
 }
 
 static inline void ice_set_ring_xdp(struct ice_tx_ring *ring)

drivers/net/ethernet/intel/ice/ice_main.c

@@ -2758,8 +2758,10 @@ int ice_destroy_xdp_rings(struct ice_vsi *vsi)
 
 	ice_for_each_xdp_txq(vsi, i)
 		if (vsi->xdp_rings[i]) {
-			if (vsi->xdp_rings[i]->desc)
+			if (vsi->xdp_rings[i]->desc) {
+				synchronize_rcu();
 				ice_free_tx_ring(vsi->xdp_rings[i]);
+			}
 			kfree_rcu(vsi->xdp_rings[i], rcu);
 			vsi->xdp_rings[i] = NULL;
 		}

drivers/net/ethernet/intel/ice/ice_xsk.c

@@ -41,8 +41,10 @@ static void ice_qp_reset_stats(struct ice_vsi *vsi, u16 q_idx)
 static void ice_qp_clean_rings(struct ice_vsi *vsi, u16 q_idx)
 {
 	ice_clean_tx_ring(vsi->tx_rings[q_idx]);
-	if (ice_is_xdp_ena_vsi(vsi))
+	if (ice_is_xdp_ena_vsi(vsi)) {
+		synchronize_rcu();
 		ice_clean_tx_ring(vsi->xdp_rings[q_idx]);
+	}
 	ice_clean_rx_ring(vsi->rx_rings[q_idx]);
 }