netdev - Re: [PATCH net-next 2/2] net: bcmgenet: add support for xmit

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Message-ID: <CAGVrzcYKYGtGWdUGK8OW_DeWba2OG78t+SObwsQPMARtz_aHvA@mail.gmail.com>
Date:	Mon, 9 Mar 2015 15:13:12 -0700
From:	Florian Fainelli <f.fainelli@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Petri Gynther <pgynther@...gle.com>,
	Jaedon Shin <jaedon.shin@...il.com>
Subject: Re: [PATCH net-next 2/2] net: bcmgenet: add support for xmit_more

2015-03-09 15:10 GMT-07:00 Eric Dumazet <eric.dumazet@...il.com>:
> On Mon, 2015-03-09 at 14:52 -0700, Florian Fainelli wrote:
>> Delay the update of the TDMA producer index unless this is the last SKB in a
>> batch, or the queue is already stopped.
>>
>> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
>> ---
>>  drivers/net/ethernet/broadcom/genet/bcmgenet.c | 6 ++++--
>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
>> index 9b3b8a3db59b..8419826da6a7 100644
>> --- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
>> +++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
>> @@ -1316,8 +1316,10 @@ static netdev_tx_t bcmgenet_xmit(struct sk_buff *skb, struct net_device *dev)
>>       ring->prod_index += nr_frags + 1;
>>       ring->prod_index &= DMA_P_INDEX_MASK;
>>
>> -     bcmgenet_tdma_ring_writel(priv, ring->index,
>> -                               ring->prod_index, TDMA_PROD_INDEX);
>> +     if (!skb->xmit_more || netif_xmit_stopped(txq))
>> +             /* Packets are ready, update producer index */
>> +             bcmgenet_tdma_ring_writel(priv, ring->index,
>> +                                       ring->prod_index, TDMA_PROD_INDEX);
>>
>>       if (ring->free_bds <= (MAX_SKB_FRAGS + 1))
>>               netif_tx_stop_queue(txq);
>
> It seems you have a race here, if you stop the queue right now, while
> this skb had skb->xmit_more set.

bcmgenet_xmit() and bcmgenet_tx_reclaim() are the only two functions
that can stop a queue, and they are using a spinlock to avoid that.
--
Florian
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