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net: ethernet: ti: cpsw: fix net watchdog timeout 

[ Upstream commit 62f94c2101 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
pull/10/head
Grygorii Strashko 2018-02-06 19:17:06 -06:00 committed by Greg Kroah-Hartman
parent 94870df33c
commit da260080c2
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

@ -1618,6 +1618,7 @@ 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");
@ -1628,15 +1629,26 @@ 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;
}