[PATCH net 0/4] bnxt: Tx NAPI disabling resiliency improvements

We can't take the tx lock from the napi poll routine, because
netpoll can poll napi at any moment, including with the tx lock
already held.

It seems that the tx lock is only protecting against the disable
path, appropriate barriers are already in place to make sure
cleanup can safely run concurrently with start_xmit. I don't see
any other reason why 'stopped && avail > thresh' needs to be
re-checked under the lock.

Remove the tx lock and use synchronize_net() to make sure
closing the device does not race we restarting the queues.
Annotate accesses to dev_state against data races.

Fixes: c0c050c58d84 ("bnxt_en: New Broadcom ethernet driver.")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 drivers/net/ethernet/broadcom/bnxt/bnxt.c | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
index 865fcb8cf29f..07827d6b0fec 100644
--- a/drivers/net/ethernet/broadcom/bnxt/bnxt.c
+++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.c

@@ -730,15 +730,10 @@ static void bnxt_tx_int(struct bnxt *bp, struct bnxt_napi *bnapi, int nr_pkts)
         */
        smp_mb();

-       if (unlikely(netif_tx_queue_stopped(txq)) &&
-           (bnxt_tx_avail(bp, txr) > bp->tx_wake_thresh)) {
-               __netif_tx_lock(txq, smp_processor_id());
-               if (netif_tx_queue_stopped(txq) &&
-                   bnxt_tx_avail(bp, txr) > bp->tx_wake_thresh &&
-                   txr->dev_state != BNXT_DEV_STATE_CLOSING)
-                       netif_tx_wake_queue(txq);
-               __netif_tx_unlock(txq);
-       }
+       if (netif_tx_queue_stopped(txq) &&

+           bnxt_tx_avail(bp, txr) > bp->tx_wake_thresh &&
+           READ_ONCE(txr->dev_state) != BNXT_DEV_STATE_CLOSING)
+               netif_tx_wake_queue(txq);
 }

 static struct page *__bnxt_alloc_rx_page(struct bnxt *bp, dma_addr_t *mapping,

@@ -9264,9 +9259,11 @@ void bnxt_tx_disable(struct bnxt *bp)
        if (bp->tx_ring) {
                for (i = 0; i < bp->tx_nr_rings; i++) {
                        txr = &bp->tx_ring[i];
-                       txr->dev_state = BNXT_DEV_STATE_CLOSING;
+                       WRITE_ONCE(txr->dev_state, BNXT_DEV_STATE_CLOSING);
                }
        }
+       /* Make sure napi polls see @dev_state change */
+       synchronize_net();
        /* Drop carrier first to prevent TX timeout */
        netif_carrier_off(bp->dev);
        /* Stop all TX queues */

@@ -9280,8 +9277,10 @@ void bnxt_tx_enable(struct bnxt *bp)

        for (i = 0; i < bp->tx_nr_rings; i++) {
                txr = &bp->tx_ring[i];
-               txr->dev_state = 0;
+               WRITE_ONCE(txr->dev_state, 0);
        }
+       /* Make sure napi polls see @dev_state change */
+       synchronize_net();
        netif_tx_wake_all_queues(bp->dev);
        if (bp->link_info.link_up)
                netif_carrier_on(bp->dev);
--

2.31.1

diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
index 865fcb8cf29f..07827d6b0fec 100644
--- a/drivers/net/ethernet/broadcom/bnxt/bnxt.c
+++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.c

@@ -730,15 +730,10 @@ static void bnxt_tx_int(struct bnxt *bp, struct bnxt_napi *bnapi, int nr_pkts)
         */
        smp_mb();

-       if (unlikely(netif_tx_queue_stopped(txq)) &&
-           (bnxt_tx_avail(bp, txr) > bp->tx_wake_thresh)) {
-               __netif_tx_lock(txq, smp_processor_id());
-               if (netif_tx_queue_stopped(txq) &&
-                   bnxt_tx_avail(bp, txr) > bp->tx_wake_thresh &&
-                   txr->dev_state != BNXT_DEV_STATE_CLOSING)
-                       netif_tx_wake_queue(txq);
-               __netif_tx_unlock(txq);
-       }
+       if (netif_tx_queue_stopped(txq) &&
+           bnxt_tx_avail(bp, txr) > bp->tx_wake_thresh &&
+           READ_ONCE(txr->dev_state) != BNXT_DEV_STATE_CLOSING)

diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
index 2c0240ee2105..b80ed556c28b 100644
--- a/drivers/net/ethernet/broadcom/bnxt/bnxt.c
+++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.c

@@ -367,6 +367,13 @@ static u16 bnxt_xmit_get_cfa_action(struct sk_buff *skb)
        return md_dst->u.port_info.port_id;
 }

+static void bnxt_txr_db_kick(struct bnxt *bp, struct bnxt_tx_ring_info *txr,
+                            u16 prod)
+{
+       bnxt_db_write(bp, &txr->tx_db, prod);
+       txr->kick_pending = 0;
+}
+
 static netdev_tx_t bnxt_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
        struct bnxt *bp = netdev_priv(dev);

@@ -396,6 +403,8 @@ static netdev_tx_t bnxt_start_xmit(struct sk_buff *skb, struct net_device *dev)
        free_size = bnxt_tx_avail(bp, txr);
        if (unlikely(free_size < skb_shinfo(skb)->nr_frags + 2)) {
                netif_tx_stop_queue(txq);
+               if (net_ratelimit())
+                       netdev_warn(dev, "bnxt: ring busy!\n");
                return NETDEV_TX_BUSY;
        }

@@ -516,21 +525,16 @@ static netdev_tx_t bnxt_start_xmit(struct sk_buff *skb, struct net_device *dev)
 normal_tx:
        if (length < BNXT_MIN_PKT_SIZE) {
                pad = BNXT_MIN_PKT_SIZE - length;
-               if (skb_pad(skb, pad)) {
+               if (skb_pad(skb, pad))
                        /* SKB already freed. */
-                       tx_buf->skb = NULL;
-                       return NETDEV_TX_OK;
-               }
+                       goto tx_kick_pending;
                length = BNXT_MIN_PKT_SIZE;
        }

        mapping = dma_map_single(&pdev->dev, skb->data, len, DMA_TO_DEVICE);

-       if (unlikely(dma_mapping_error(&pdev->dev, mapping))) {
-               dev_kfree_skb_any(skb);
-               tx_buf->skb = NULL;
-               return NETDEV_TX_OK;
-       }
+       if (unlikely(dma_mapping_error(&pdev->dev, mapping)))
+               goto tx_free;

        dma_unmap_addr_set(tx_buf, mapping, mapping);
        flags = (len << TX_BD_LEN_SHIFT) | TX_BD_TYPE_LONG_TX_BD |

@@ -617,13 +621,15 @@ static netdev_tx_t bnxt_start_xmit(struct sk_buff *skb, struct net_device *dev)
        txr->tx_prod = prod;

        if (!netdev_xmit_more() || netif_xmit_stopped(txq))
-               bnxt_db_write(bp, &txr->tx_db, prod);
+               bnxt_txr_db_kick(bp, txr, prod);
+       else
+               txr->kick_pending = 1;

 tx_done:

        if (unlikely(bnxt_tx_avail(bp, txr) <= MAX_SKB_FRAGS + 1)) {
                if (netdev_xmit_more() && !tx_buf->is_push)
-                       bnxt_db_write(bp, &txr->tx_db, prod);
+                       bnxt_txr_db_kick(bp, txr, prod);

                netif_tx_stop_queue(txq);

@@ -661,7 +667,12 @@ static netdev_tx_t bnxt_start_xmit(struct sk_buff *skb, struct net_device *dev)
                               PCI_DMA_TODEVICE);
        }

+tx_free:
        dev_kfree_skb_any(skb);
+tx_kick_pending:
+       tx_buf->skb = NULL;
+       if (txr->kick_pending)
+               bnxt_txr_db_kick(bp, txr, prod);