netdev - Re: [PATCH v3 6/6] net: sh

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Message-Id: <20120515.130552.119728053706080493.davem@davemloft.net>
Date:	Tue, 15 May 2012 13:05:52 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	yoshihiro.shimoda.uh@...esas.com
Cc:	netdev@...r.kernel.org, linux-sh@...r.kernel.org
Subject: Re: [PATCH v3 6/6] net: sh_eth: use NAPI

From: "Shimoda, Yoshihiro" <yoshihiro.shimoda.uh@...esas.com>
Date: Tue, 15 May 2012 18:46:25 +0900

> 2012/05/15 14:07, David Miller wrote:
>> From: "Shimoda, Yoshihiro" <yoshihiro.shimoda.uh@...esas.com>
>> Date: Tue, 15 May 2012 13:47:44 +0900
>> 
>>> 2012/05/15 7:50, David Miller wrote:
>>>> You need strict synchronization between your TX queueing and TX
>>>> liberation flows.  So that queue stop and wake are only performed
>>>> at the correct moment.
>>>
>>> I will add netif_queue_stopped() in the sh_eth_poll().
>> 
>> That doesn't fix the bug.  What if someone transmits a packet and
>> fills the TX queue between the netif_queue_stopped() test and the
>> call to netif_wake_queue()?
>> 
>> Adding another test doesn't create the necessary synchronization.
>> 
> 
> Thank you for the reply again.
> I will modify the code as the following. Is it correct?
> 
> 	if (txfree_num) {
> 		netif_tx_lock(ndev);
> 		if (netif_queue_stopped(ndev))
> 			netif_wake_queue(ndev);
> 		netif_tx_unlock(ndev);
> 	}

Yes, and then you don't need that private lock in the start_xmit()
method at all, since that method runs with the tx_lock held.
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