bnxt_en: Prevent XDP redirect from running when stopping TX queue

Add checks in the XDP redirect callback to prevent XDP from running when
the TX ring is undergoing shutdown.

Also remove redundant checks in the XDP redirect callback to validate the
txr and the flag that indicates the ring supports XDP. The modulo
arithmetic on 'tx_nr_rings_xdp' already guarantees the derived TX
ring is an XDP ring.  txr is also guaranteed to be valid after checking
BNXT_STATE_OPEN and within RCU grace period.

Fixes: f18c2b7 ("bnxt_en: optimized XDP_REDIRECT support")
Reviewed-by: Vladimir Olovyannikov <[email protected]>
Signed-off-by: Ray Jui <[email protected]>
Signed-off-by: Michael Chan <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c

@@ -229,14 +229,16 @@ int bnxt_xdp_xmit(struct net_device *dev, int num_frames,
 	ring = smp_processor_id() % bp->tx_nr_rings_xdp;
 	txr = &bp->tx_ring[ring];
 
+	if (READ_ONCE(txr->dev_state) == BNXT_DEV_STATE_CLOSING)
+		return -EINVAL;
+
 	if (static_branch_unlikely(&bnxt_xdp_locking_key))
 		spin_lock(&txr->xdp_tx_lock);
 
 	for (i = 0; i < num_frames; i++) {
 		struct xdp_frame *xdp = frames[i];
 
-		if (!txr || !bnxt_tx_avail(bp, txr) ||
-		    !(bp->bnapi[ring]->flags & BNXT_NAPI_FLAG_XDP))
+		if (!bnxt_tx_avail(bp, txr))
 			break;
 
 		mapping = dma_map_single(&pdev->dev, xdp->data, xdp->len,