Re: [PATCH 1/3] net: lpc_eth: Replace WARN() trace with simple pr_warn()

Eric Dumazet
2012-06-11T08:54:01Z

On Mon, 2012-06-11 at 10:36 +0200, Roland Stigge wrote:

> I encountered cases where this happened for me on a custom board under
> heavy load.
>
> I discussed this with Kevin Wells, the original driver author. We
> identified the case of xmit()'s TX request (from .ndo_start_xmit) with
> full TX driver buffers as valid when ethernet is busy.
>
> But maybe this is wrong. Can you please give me a hint how the net
> subsystem makes sure that this doesn't happen under normal circumstances?

When TX ring is about to be filler, driver lpc_eth_hard_start_xmit()
calls netif_stop_queue(ndev);

So network stack should not call again lpc_eth_hard_start_xmit().

I would say the bug(s) come from __lpc_handle_xmit(), since it does :

if (netif_queue_stopped(ndev))
netif_wake_queue(ndev);

without making sure some room is available in TX ring.

cumulative patch :

diff --git a/drivers/net/ethernet/nxp/lpc_eth.c b/drivers/net/ethernet/nxp/lpc_eth.c
index 8d2666f..59b37c8 100644
--- a/drivers/net/ethernet/nxp/lpc_eth.c
+++ b/drivers/net/ethernet/nxp/lpc_eth.c
@@ -946,16 +946,16 @@ static void __lpc_handle_xmit(struct net_device *ndev)
/* Update stats */
ndev->stats.tx_packets++;
ndev->stats.tx_bytes += skb->len;
-
- /* Free buffer */
- dev_kfree_skb_irq(skb);
}
+ dev_kfree_skb_irq(skb);

txcidx = readl(LPC_ENET_TXCONSUMEINDEX(pldat->net_base));
}

- if (netif_queue_stopped(ndev))
- netif_wake_queue(ndev);
+ if (pldat->num_used_tx_buffs <= ENET_TX_DESC/2) {
+ if (netif_queue_stopped(ndev))
+ netif_wake_queue(ndev);
+ }
}

static int __lpc_handle_recv(struct net_device *ndev, int budget)