From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH 1/3] net: lpc_eth: Replace WARN() trace with simple pr_warn() Date: Mon, 11 Jun 2012 10:53:55 +0200 Message-ID: <1339404835.6001.1788.camel@edumazet-glaptop> References: <1339401793-12258-1-git-send-email-stigge@antcom.de> <1339403108.6001.1697.camel@edumazet-glaptop> <4FD5AE1D.9030807@antcom.de> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: davem@davemloft.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kevin.wells@nxp.com, srinivas.bakki@nxp.com, aletes.xgr@gmail.com, linux-arm-kernel@lists.infradead.org To: Roland Stigge Return-path: In-Reply-To: <4FD5AE1D.9030807@antcom.de> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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)