From 62f94c2101f35cd45775df00ba09bde77580e26a Mon Sep 17 00:00:00 2001 From: Grygorii Strashko Date: Tue, 6 Feb 2018 19:17:06 -0600 Subject: net: ethernet: ti: cpsw: fix net watchdog timeout It was discovered that simple program which indefinitely sends 200b UDP packets and runs on TI AM574x SoC (SMP) under RT Kernel triggers network watchdog timeout in TI CPSW driver (<6 hours run). The network watchdog timeout is triggered due to race between cpsw_ndo_start_xmit() and cpsw_tx_handler() [NAPI] cpsw_ndo_start_xmit() if (unlikely(!cpdma_check_free_tx_desc(txch))) { txq = netdev_get_tx_queue(ndev, q_idx); netif_tx_stop_queue(txq); ^^ as per [1] barier has to be used after set_bit() otherwise new value might not be visible to other cpus } cpsw_tx_handler() if (unlikely(netif_tx_queue_stopped(txq))) netif_tx_wake_queue(txq); and when it happens ndev TX queue became disabled forever while driver's HW TX queue is empty. Fix this, by adding smp_mb__after_atomic() after netif_tx_stop_queue() calls and double check for free TX descriptors after stopping ndev TX queue - if there are free TX descriptors wake up ndev TX queue. [1] https://www.kernel.org/doc/html/latest/core-api/atomic_ops.html Signed-off-by: Grygorii Strashko Reviewed-by: Ivan Khoronzhuk Signed-off-by: David S. Miller --- drivers/net/ethernet/ti/cpsw.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) (limited to 'drivers/net') diff --git a/drivers/net/ethernet/ti/cpsw.c b/drivers/net/ethernet/ti/cpsw.c index 3c85a0885f9b..1b1b78fdc138 100644 --- a/drivers/net/ethernet/ti/cpsw.c +++ b/drivers/net/ethernet/ti/cpsw.c @@ -1636,6 +1636,7 @@ static netdev_tx_t cpsw_ndo_start_xmit(struct sk_buff *skb, q_idx = q_idx % cpsw->tx_ch_num; txch = cpsw->txv[q_idx].ch; + txq = netdev_get_tx_queue(ndev, q_idx); ret = cpsw_tx_packet_submit(priv, skb, txch); if (unlikely(ret != 0)) { cpsw_err(priv, tx_err, "desc submit failed\n"); @@ -1646,15 +1647,26 @@ static netdev_tx_t cpsw_ndo_start_xmit(struct sk_buff *skb, * tell the kernel to stop sending us tx frames. */ if (unlikely(!cpdma_check_free_tx_desc(txch))) { - txq = netdev_get_tx_queue(ndev, q_idx); netif_tx_stop_queue(txq); + + /* Barrier, so that stop_queue visible to other cpus */ + smp_mb__after_atomic(); + + if (cpdma_check_free_tx_desc(txch)) + netif_tx_wake_queue(txq); } return NETDEV_TX_OK; fail: ndev->stats.tx_dropped++; - txq = netdev_get_tx_queue(ndev, skb_get_queue_mapping(skb)); netif_tx_stop_queue(txq); + + /* Barrier, so that stop_queue visible to other cpus */ + smp_mb__after_atomic(); + + if (cpdma_check_free_tx_desc(txch)) + netif_tx_wake_queue(txq); + return NETDEV_TX_BUSY; } -- cgit v1.2.3