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

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Message-ID: <4FD5AE1D.9030807@antcom.de>
Date:	Mon, 11 Jun 2012 10:36:45 +0200
From:	Roland Stigge <stigge@...com.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, kevin.wells@....com,
	srinivas.bakki@....com, aletes.xgr@...il.com,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/3] net: lpc_eth: Replace WARN() trace with simple pr_warn()

Hi Dave and Eric,

thanks for your feedback!

On 06/11/2012 10:25 AM, Eric Dumazet wrote:
> On Mon, 2012-06-11 at 10:03 +0200, Roland Stigge wrote:
>> A WARN() trace indicating a "BUG!" was identified as a "normal" case in the
>> xmit function in case all TX descriptors are occupied already. In this case,
>> NETDEV_TX_BUSY is returned, nothing buggy at all.
>>
>> Signed-off-by: Roland Stigge <stigge@...com.de>
>> Tested-by: Alexandre Pereira da Silva <aletes.xgr@...il.com>
>>
>> ---
>>  drivers/net/ethernet/nxp/lpc_eth.c |    2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> --- linux-2.6.orig/drivers/net/ethernet/nxp/lpc_eth.c
>> +++ linux-2.6/drivers/net/ethernet/nxp/lpc_eth.c
>> @@ -1114,7 +1114,7 @@ static int lpc_eth_hard_start_xmit(struc
>>  		   buffers */
>>  		netif_stop_queue(ndev);
>>  		spin_unlock_irq(&pldat->lock);
>> -		WARN(1, "BUG! TX request when no free TX buffers!\n");
>> +		pr_warn("Note: TX request when no free TX buffers.\n");
>>  		return NETDEV_TX_BUSY;
>>  	}
>>  
> 
> Entering this path is a bug, don't hide it...
> 
> Please share with us how this bug was identified as a "normal case" ?

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?

Thanks in advance!

Roland
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