[PATCH net-next 0/4] net: make dev_watchdog() less intrusive

@@ -592,7 +592,7 @@ struct netdev_queue {
 	 * Number of TX timeouts for this queue
 	 * (/sys/class/net/DEV/Q/trans_timeout)
 	 */
-	unsigned long		trans_timeout;
+	atomic_long_t		trans_timeout;
 
 	/* Subordinate device that the queue has been assigned to */
 	struct net_device	*sb_dev;

@@ -1201,11 +1201,7 @@ static const struct sysfs_ops netdev_queue_sysfs_ops = {
 
 static ssize_t tx_timeout_show(struct netdev_queue *queue, char *buf)
 {
-	unsigned long trans_timeout;
-
-	spin_lock_irq(&queue->_xmit_lock);
-	trans_timeout = queue->trans_timeout;
-	spin_unlock_irq(&queue->_xmit_lock);
+	unsigned long trans_timeout = atomic_long_read(&queue->trans_timeout);
 
 	return sprintf(buf, fmt_ulong, trans_timeout);
 }

@@ -467,7 +467,7 @@ static void dev_watchdog(struct timer_list *t)
 				    time_after(jiffies, (trans_start +
 							 dev->watchdog_timeo))) {
 					some_queue_timedout = 1;
-					txq->trans_timeout++;
+					atomic_long_inc(&txq->trans_timeout);
 					break;
 				}
 			}

@@ -869,7 +869,7 @@ static void xgene_enet_timeout(struct net_device *ndev, unsigned int txqueue)
 
 	for (i = 0; i < pdata->txq_cnt; i++) {
 		txq = netdev_get_tx_queue(ndev, i);
-		txq->trans_start = jiffies;
+		txq_trans_cond_update(txq);
 		netif_tx_start_queue(txq);
 	}
 }

@@ -766,7 +766,7 @@ static bool ag71xx_check_dma_stuck(struct ag71xx *ag)
 	unsigned long timestamp;
 	u32 rx_sm, tx_sm, rx_fd;
 
-	timestamp = netdev_get_tx_queue(ag->ndev, 0)->trans_start;
+	timestamp = READ_ONCE(netdev_get_tx_queue(ag->ndev, 0)->trans_start);
 	if (likely(time_before(jiffies, timestamp + HZ / 10)))
 		return false;
 

@@ -2325,7 +2325,7 @@ dpaa_start_xmit(struct sk_buff *skb, struct net_device *net_dev)
 	txq = netdev_get_tx_queue(net_dev, queue_mapping);
 
 	/* LLTX requires to do our own update of trans_start */
-	txq->trans_start = jiffies;
+	txq_trans_cond_update(txq);
 
 	if (priv->tx_tstamp && skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP) {
 		fd.cmd |= cpu_to_be32(FM_FD_CMD_UPD);

@@ -2531,7 +2531,7 @@ static int dpaa_xdp_xmit_frame(struct net_device *net_dev,
 
 	/* Bump the trans_start */
 	txq = netdev_get_tx_queue(net_dev, smp_processor_id());
-	txq->trans_start = jiffies;
+	txq_trans_cond_update(txq);
 
 	err = dpaa_xmit(priv, percpu_stats, smp_processor_id(), &fd);
 	if (err) {

@@ -2679,7 +2679,7 @@ static bool hns3_get_tx_timeo_queue_info(struct net_device *ndev)
 		unsigned long trans_start;
 
 		q = netdev_get_tx_queue(ndev, i);
-		trans_start = q->trans_start;
+		trans_start = READ_ONCE(q->trans_start);
 		if (netif_xmit_stopped(q) &&
 		    time_after(jiffies,
 			       (trans_start + ndev->watchdog_timeo))) {

@@ -2058,7 +2058,7 @@ static netdev_tx_t ibmvnic_xmit(struct sk_buff *skb, struct net_device *netdev)
 
 	tx_packets++;
 	tx_bytes += skb->len;
-	txq->trans_start = jiffies;
+	txq_trans_cond_update(txq);
 	ret = NETDEV_TX_OK;
 	goto out;
 

@@ -2927,7 +2927,7 @@ static int igb_xdp_xmit_back(struct igb_adapter *adapter, struct xdp_buff *xdp)
 	nq = txring_txq(tx_ring);
 	__netif_tx_lock(nq, cpu);
 	/* Avoid transmit queue timeout since we share it with the slow path */
-	nq->trans_start = jiffies;
+	txq_trans_cond_update(nq);
 	ret = igb_xmit_xdp_ring(adapter, tx_ring, xdpf);
 	__netif_tx_unlock(nq);
 

@@ -2961,7 +2961,7 @@ static int igb_xdp_xmit(struct net_device *dev, int n,
 	__netif_tx_lock(nq, cpu);
 
 	/* Avoid transmit queue timeout since we share it with the slow path */
-	nq->trans_start = jiffies;
+	txq_trans_cond_update(nq);
 
 	for (i = 0; i < n; i++) {
 		struct xdp_frame *xdpf = frames[i];

@@ -565,7 +565,7 @@ int mlx5e_reporter_tx_timeout(struct mlx5e_txqsq *sq)
 	snprintf(err_str, sizeof(err_str),
 		 "TX timeout on queue: %d, SQ: 0x%x, CQ: 0x%x, SQ Cons: 0x%x SQ Prod: 0x%x, usecs since last trans: %u",
 		 sq->ch_ix, sq->sqn, sq->cq.mcq.cqn, sq->cc, sq->pc,
-		 jiffies_to_usecs(jiffies - sq->txq->trans_start));
+		 jiffies_to_usecs(jiffies - READ_ONCE(sq->txq->trans_start)));
 
 	mlx5e_health_report(priv, priv->tx_reporter, err_str, &err_ctx);
 	return to_ctx.status;

@@ -2356,7 +2356,7 @@ static bool stmmac_xdp_xmit_zc(struct stmmac_priv *priv, u32 queue, u32 budget)
 	bool work_done = true;
 
 	/* Avoids TX time-out as we are sharing with slow path */
-	nq->trans_start = jiffies;
+	txq_trans_cond_update(nq->trans_start);
 
 	budget = min(budget, stmmac_tx_avail(priv, queue));
 

@@ -4657,7 +4657,7 @@ static int stmmac_xdp_xmit_back(struct stmmac_priv *priv,
 
 	__netif_tx_lock(nq, cpu);
 	/* Avoids TX time-out as we are sharing with slow path */
-	nq->trans_start = jiffies;
+	txq_trans_cond_update(nq->trans_start);
 
 	res = stmmac_xdp_xmit_xdpf(priv, queue, xdpf, false);
 	if (res == STMMAC_XDP_TX)

@@ -6293,7 +6293,7 @@ static int stmmac_xdp_xmit(struct net_device *dev, int num_frames,
 
 	__netif_tx_lock(nq, cpu);
 	/* Avoids TX time-out as we are sharing with slow path */
-	nq->trans_start = jiffies;
+	txq_trans_cond_update(nq);
 
 	for (i = 0; i < num_frames; i++) {
 		int res;

@@ -345,7 +345,7 @@ static void am65_cpsw_nuss_ndo_host_tx_timeout(struct net_device *ndev,
 
 	netif_txq = netdev_get_tx_queue(ndev, txqueue);
 	tx_chn = &common->tx_chns[txqueue];
-	trans_start = netif_txq->trans_start;
+	trans_start = READ_ONCE(netif_txq->trans_start);
 
 	netdev_err(ndev, "txq:%d DRV_XOFF:%d tmo:%u dql_avail:%d free_desc:%zu\n",
 		   txqueue,

@@ -2694,7 +2694,7 @@ static void virtnet_tx_timeout(struct net_device *dev, unsigned int txqueue)
 
 	netdev_err(dev, "TX timeout on queue: %u, sq: %s, vq: 0x%x, name: %s, %u usecs ago\n",
 		   txqueue, sq->name, sq->vq->index, sq->vq->name,
-		   jiffies_to_usecs(jiffies - txq->trans_start));
+		   jiffies_to_usecs(jiffies - READ_ONCE(txq->trans_start)));
 }
 
 static const struct net_device_ops virtnet_netdev = {

@@ -332,7 +332,7 @@ void mwifiex_set_trans_start(struct net_device *dev)
 	int i;
 
 	for (i = 0; i < dev->num_tx_queues; i++)
-		netdev_get_tx_queue(dev, i)->trans_start = jiffies;
+		txq_trans_cond_update(netdev_get_tx_queue(dev, i));
 
 	netif_trans_update(dev);
 }

@@ -2515,7 +2515,7 @@ void rtllib_stop_all_queues(struct rtllib_device *ieee)
 	unsigned int i;
 
 	for (i = 0; i < ieee->dev->num_tx_queues; i++)
-		netdev_get_tx_queue(ieee->dev, i)->trans_start = jiffies;
+		txq_trans_cond_update(netdev_get_tx_queue(ieee->dev, i));
 
 	netif_tx_stop_all_queues(ieee->dev);
 }

@@ -4095,10 +4095,21 @@ static inline void __netif_tx_unlock_bh(struct netdev_queue *txq)
 	spin_unlock_bh(&txq->_xmit_lock);
 }
 
+/*
+ * txq->trans_start can be read locklessly from dev_watchdog()
+ */
 static inline void txq_trans_update(struct netdev_queue *txq)
 {
 	if (txq->xmit_lock_owner != -1)
-		txq->trans_start = jiffies;
+		WRITE_ONCE(txq->trans_start, jiffies);
+}
+
+static inline void txq_trans_cond_update(struct netdev_queue *txq)
+{
+	unsigned long now = jiffies;
+
+	if (READ_ONCE(txq->trans_start) != now)
+		WRITE_ONCE(txq->trans_start, now);
 }
 
 /* legacy drivers only, netdev_start_xmit() sets txq->trans_start */

@@ -4106,8 +4117,7 @@ static inline void netif_trans_update(struct net_device *dev)
 {
 	struct netdev_queue *txq = netdev_get_tx_queue(dev, 0);
 
-	if (txq->trans_start != jiffies)
-		txq->trans_start = jiffies;
+	txq_trans_cond_update(txq);
 }
 
 /**

@@ -434,9 +434,9 @@ unsigned long dev_trans_start(struct net_device *dev)
 		dev = vlan_dev_real_dev(dev);
 	else if (netif_is_macvlan(dev))
 		dev = macvlan_dev_real_dev(dev);
-	res = netdev_get_tx_queue(dev, 0)->trans_start;
+	res = READ_ONCE(netdev_get_tx_queue(dev, 0)->trans_start);
 	for (i = 1; i < dev->num_tx_queues; i++) {
-		val = netdev_get_tx_queue(dev, i)->trans_start;
+		val = READ_ONCE(netdev_get_tx_queue(dev, i)->trans_start);
 		if (val && time_after(val, res))
 			res = val;
 	}

@@ -462,7 +462,7 @@ static void dev_watchdog(struct timer_list *t)
 				struct netdev_queue *txq;
 
 				txq = netdev_get_tx_queue(dev, i);
-				trans_start = txq->trans_start;
+				trans_start = READ_ONCE(txq->trans_start);
 				if (netif_xmit_stopped(txq) &&
 				    time_after(jiffies, (trans_start +
 							 dev->watchdog_timeo))) {

@@ -1148,7 +1148,7 @@ static void transition_one_qdisc(struct net_device *dev,
 
 	rcu_assign_pointer(dev_queue->qdisc, new_qdisc);
 	if (need_watchdog_p) {
-		dev_queue->trans_start = 0;
+		WRITE_ONCE(dev_queue->trans_start, 0);
 		*need_watchdog_p = 1;
 	}
 }

@@ -4126,27 +4126,7 @@ static inline void netif_trans_update(struct net_device *dev)
  *
  * Get network device transmit lock
  */
-static inline void netif_tx_lock(struct net_device *dev)
-{
-	unsigned int i;
-	int cpu;
-
-	spin_lock(&dev->tx_global_lock);
-	cpu = smp_processor_id();
-	for (i = 0; i < dev->num_tx_queues; i++) {
-		struct netdev_queue *txq = netdev_get_tx_queue(dev, i);
-
-		/* We are the only thread of execution doing a
-		 * freeze, but we have to grab the _xmit_lock in
-		 * order to synchronize with threads which are in
-		 * the ->hard_start_xmit() handler and already
-		 * checked the frozen bit.
-		 */
-		__netif_tx_lock(txq, cpu);
-		set_bit(__QUEUE_STATE_FROZEN, &txq->state);
-		__netif_tx_unlock(txq);
-	}
-}
+void netif_tx_lock(struct net_device *dev);
 
 static inline void netif_tx_lock_bh(struct net_device *dev)
 {

@@ -4154,22 +4134,7 @@ static inline void netif_tx_lock_bh(struct net_device *dev)
 	netif_tx_lock(dev);
 }
 
-static inline void netif_tx_unlock(struct net_device *dev)
-{
-	unsigned int i;
-
-	for (i = 0; i < dev->num_tx_queues; i++) {
-		struct netdev_queue *txq = netdev_get_tx_queue(dev, i);
-
-		/* No need to grab the _xmit_lock here.  If the
-		 * queue is not stopped for another reason, we
-		 * force a schedule.
-		 */
-		clear_bit(__QUEUE_STATE_FROZEN, &txq->state);
-		netif_schedule_queue(txq);
-	}
-	spin_unlock(&dev->tx_global_lock);
-}
+void netif_tx_unlock(struct net_device *dev);
 
 static inline void netif_tx_unlock_bh(struct net_device *dev)
 {

@@ -445,6 +445,57 @@ unsigned long dev_trans_start(struct net_device *dev)
 }
 EXPORT_SYMBOL(dev_trans_start);
 
+static void netif_freeze_queues(struct net_device *dev)
+{
+	unsigned int i;
+	int cpu;
+
+	cpu = smp_processor_id();
+	for (i = 0; i < dev->num_tx_queues; i++) {
+		struct netdev_queue *txq = netdev_get_tx_queue(dev, i);
+
+		/* We are the only thread of execution doing a
+		 * freeze, but we have to grab the _xmit_lock in
+		 * order to synchronize with threads which are in
+		 * the ->hard_start_xmit() handler and already
+		 * checked the frozen bit.
+		 */
+		__netif_tx_lock(txq, cpu);
+		set_bit(__QUEUE_STATE_FROZEN, &txq->state);
+		__netif_tx_unlock(txq);
+	}
+}
+
+void netif_tx_lock(struct net_device *dev)
+{
+	spin_lock(&dev->tx_global_lock);
+	netif_freeze_queues(dev);
+}
+EXPORT_SYMBOL(netif_tx_lock);
+
+static void netif_unfreeze_queues(struct net_device *dev)
+{
+	unsigned int i;
+
+	for (i = 0; i < dev->num_tx_queues; i++) {
+		struct netdev_queue *txq = netdev_get_tx_queue(dev, i);
+
+		/* No need to grab the _xmit_lock here.  If the
+		 * queue is not stopped for another reason, we
+		 * force a schedule.
+		 */
+		clear_bit(__QUEUE_STATE_FROZEN, &txq->state);
+		netif_schedule_queue(txq);
+	}
+}
+
+void netif_tx_unlock(struct net_device *dev)
+{
+	netif_unfreeze_queues(dev);
+	spin_unlock(&dev->tx_global_lock);
+}
+EXPORT_SYMBOL(netif_tx_unlock);
+
 static void dev_watchdog(struct timer_list *t)
 {
 	struct net_device *dev = from_timer(dev, t, watchdog_timer);

@@ -500,7 +500,7 @@ static void dev_watchdog(struct timer_list *t)
 {
 	struct net_device *dev = from_timer(dev, t, watchdog_timer);
 
-	netif_tx_lock(dev);
+	spin_lock(&dev->tx_global_lock);
 	if (!qdisc_tx_is_noop(dev)) {
 		if (netif_device_present(dev) &&
 		    netif_running(dev) &&

@@ -523,11 +523,13 @@ static void dev_watchdog(struct timer_list *t)
 				}
 			}
 
-			if (some_queue_timedout) {
+			if (unlikely(some_queue_timedout)) {
 				trace_net_dev_xmit_timeout(dev, i);
 				WARN_ONCE(1, KERN_INFO "NETDEV WATCHDOG: %s (%s): transmit queue %u timed out\n",
 				       dev->name, netdev_drivername(dev), i);
+				netif_freeze_queues(dev);
 				dev->netdev_ops->ndo_tx_timeout(dev, i);
+				netif_unfreeze_queues(dev);
 			}
 			if (!mod_timer(&dev->watchdog_timer,
 				       round_jiffies(jiffies +

@@ -535,7 +537,7 @@ static void dev_watchdog(struct timer_list *t)
 				dev_hold(dev);
 		}
 	}
-	netif_tx_unlock(dev);
+	spin_unlock(&dev->tx_global_lock);
 
 	dev_put(dev);
 }