netdev - RE: [PATCH 1/3] ucc_geth: Fix empty TX queue processing

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Message-ID: <100CB1A1877FF245BDB7AF83A0E73FFE26BEC3@zch01exm28.fsl.freescale.net>
Date:	Mon, 11 Jan 2010 19:52:26 +0800
From:	"Wu Jiajun-B06378" <B06378@...escale.com>
To:	<avorontsov@...mvista.com>
Cc:	<linuxppc-dev@...abs.org>, <netdev@...r.kernel.org>,
	<lsorense@...lub.uwaterloo.ca>, <davem@...emloft.net>
Subject: RE: [PATCH 1/3] ucc_geth: Fix empty TX queue processing


Yes,'if (!skb)' is enough.
You can reproduce transmitting stopping if you use 'if ((bd == ugeth->txBd[txQ])' and run ipforwarding with MTU=64 1Gbps 100%linerate.


-----Original Message-----
From: Anton Vorontsov [mailto:avorontsov@...mvista.com] 
Sent: 2010年1月11日 18:53
To: Wu Jiajun-B06378
Cc: linuxppc-dev@...abs.org; netdev@...r.kernel.org; lsorense@...lub.uwaterloo.ca; davem@...emloft.net
Subject: Re: [PATCH 1/3] ucc_geth: Fix empty TX queue processing

On Mon, Jan 11, 2010 at 11:47:37AM +0800, Wu Jiajun-B06378 wrote:
>  
> 'bd == ugeth->txBd[txQ]' has two possible statuses: 1)full queue.
> 2)empty queue.
> Removing 'netif_queue_stopped() == 0' will make transmitting stopping 
> when the queue is full.
> 
> I made a new patch for this oops.
[...]
> +		if ((bd == ugeth->txBd[txQ]) && (skb == NULL))
>  			break;

Hm. I wonder why do we need the 'bd == ugeth->txBd[txQ]' check at all? The null skb will cause a kernel oops anyway.

I think the patch below should be sufficient for the fix.
Can you try it? Or if you tell me how to reproduce the issue you observe, I can try it myself.

Thanks a lot!

diff --git a/drivers/net/ucc_geth.c b/drivers/net/ucc_geth.c index 41ad2f3..a1a6d06 100644
--- a/drivers/net/ucc_geth.c
+++ b/drivers/net/ucc_geth.c
@@ -3279,13 +3279,12 @@ static int ucc_geth_tx(struct net_device *dev, u8 txQ)
 		/* Handle the transmitted buffer and release */
 		/* the BD to be used with the current frame  */
 
-		if (bd == ugeth->txBd[txQ]) /* queue empty? */
+		skb = ugeth->tx_skbuff[txQ][ugeth->skb_dirtytx[txQ]];
+		if (!skb)
 			break;
 
 		dev->stats.tx_packets++;
 
-		skb = ugeth->tx_skbuff[txQ][ugeth->skb_dirtytx[txQ]];
-
 		if (skb_queue_len(&ugeth->rx_recycle) < RX_BD_RING_LEN &&
 			     skb_recycle_check(skb,
 				    ugeth->ug_info->uf_info.max_rx_buf_length +

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