eth: bnxt: handle invalid Tx completions more gracefully

Invalid Tx completions should never happen (tm) but when they do
they crash the host, because driver blindly trusts that there is
a valid skb pointer on the ring.

The completions I've seen appear to be some form of FW / HW
miscalculation or staleness, they have typical (small) values
(<100), but they are most often higher than number of queued
descriptors. They usually happen after boot.

Instead of crashing, print a warning and schedule a reset.

Link: https://lore.kernel.org/r/20230720010440.1967136-4-kuba@kernel.org
Reviewed-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

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

@@ -331,6 +331,22 @@ static void bnxt_sched_reset_rxr(struct bnxt *bp, struct bnxt_rx_ring_info *rxr)
 	rxr->rx_next_cons = 0xffff;
 }
 
+void bnxt_sched_reset_txr(struct bnxt *bp, struct bnxt_tx_ring_info *txr,
+			  int idx)
+{
+	struct bnxt_napi *bnapi = txr->bnapi;
+
+	if (bnapi->tx_fault)
+		return;
+
+	netdev_err(bp->dev, "Invalid Tx completion (ring:%d tx_pkts:%d cons:%u prod:%u i:%d)",
+		   txr->txq_index, bnapi->tx_pkts,
+		   txr->tx_cons, txr->tx_prod, idx);
+	WARN_ON_ONCE(1);
+	bnapi->tx_fault = 1;
+	bnxt_queue_sp_work(bp, BNXT_RESET_TASK_SP_EVENT);
+}
+
 const u16 bnxt_lhint_arr[] = {
 	TX_BD_FLAGS_LHINT_512_AND_SMALLER,
 	TX_BD_FLAGS_LHINT_512_TO_1023,
@@ -690,6 +706,11 @@ static void bnxt_tx_int(struct bnxt *bp, struct bnxt_napi *bnapi, int nr_pkts)
 		skb = tx_buf->skb;
 		tx_buf->skb = NULL;
 
+		if (unlikely(!skb)) {
+			bnxt_sched_reset_txr(bp, txr, i);
+			return;
+		}
+
 		tx_bytes += skb->len;
 
 		if (tx_buf->is_push) {
@@ -2576,7 +2597,7 @@ static int __bnxt_poll_work(struct bnxt *bp, struct bnxt_cp_ring_info *cpr,
 
 static void __bnxt_poll_work_done(struct bnxt *bp, struct bnxt_napi *bnapi)
 {
-	if (bnapi->tx_pkts) {
+	if (bnapi->tx_pkts && !bnapi->tx_fault) {
 		bnapi->tx_int(bp, bnapi, bnapi->tx_pkts);
 		bnapi->tx_pkts = 0;
 	}
@@ -9429,6 +9450,8 @@ static void bnxt_enable_napi(struct bnxt *bp)
 		struct bnxt_napi *bnapi = bp->bnapi[i];
 		struct bnxt_cp_ring_info *cpr;
 
+		bnapi->tx_fault = 0;
+
 		cpr = &bnapi->cp_ring;
 		if (bnapi->in_reset)
 			cpr->sw_stats.rx.rx_resets++;

drivers/net/ethernet/broadcom/bnxt/bnxt.h

@@ -1008,6 +1008,7 @@ struct bnxt_napi {
 					  int);
 	int			tx_pkts;
 	u8			events;
+	u8			tx_fault:1;
 
 	u32			flags;
 #define BNXT_NAPI_FLAG_XDP	0x1
@@ -2329,6 +2330,8 @@ int bnxt_get_avail_msix(struct bnxt *bp, int num);
 int bnxt_reserve_rings(struct bnxt *bp, bool irq_re_init);
 void bnxt_tx_disable(struct bnxt *bp);
 void bnxt_tx_enable(struct bnxt *bp);
+void bnxt_sched_reset_txr(struct bnxt *bp, struct bnxt_tx_ring_info *txr,
+			  int idx);
 void bnxt_report_link(struct bnxt *bp);
 int bnxt_update_link(struct bnxt *bp, bool chng_link_state);
 int bnxt_hwrm_set_pause(struct bnxt *);

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

@@ -149,6 +149,7 @@ void bnxt_tx_int_xdp(struct bnxt *bp, struct bnxt_napi *bnapi, int nr_pkts)
 			tx_buf->action = 0;
 			tx_buf->xdpf = NULL;
 		} else if (tx_buf->action == XDP_TX) {
+			tx_buf->action = 0;
 			rx_doorbell_needed = true;
 			last_tx_cons = tx_cons;
 
@@ -158,6 +159,9 @@ void bnxt_tx_int_xdp(struct bnxt *bp, struct bnxt_napi *bnapi, int nr_pkts)
 				tx_buf = &txr->tx_buf_ring[tx_cons];
 				page_pool_recycle_direct(rxr->page_pool, tx_buf->page);
 			}
+		} else {
+			bnxt_sched_reset_txr(bp, txr, i);
+			return;
 		}
 		tx_cons = NEXT_TX(tx_cons);
 	}