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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 <grygorii.strashko@ti.com>
Reviewed-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Grygorii Strashko 2018-02-06 19:17:06 -06:00 committed by David S. Miller
parent b0992eca00
commit 62f94c2101
1 changed files with 14 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
drivers/net/ethernet/ti/cpsw.c
View File

@ -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;
}