Re: [PATCH] net: mvneta: fix handling of the Tx descriptor counter

[Andreas Tobler <andreas.tobler@cloudguard.ch>]

Hi Simon,


On 08.11.17 18:17, Simon Guinot wrote:
> Hi Sven and Andreas,
> 
> Please, can you try with this patch ?

Today we, my son and I, repeated the failing scenario and we were able 
to show that our scenario behaves stable after you patch being applied.

Thanks for taking care of this issue. If you need further testing let me 
know.

Regards,
Andreas

> On Wed, Nov 08, 2017 at 05:58:35PM +0100, Simon Guinot wrote:
>> The mvneta controller provides a 8-bit register to update the pending
>> Tx descriptor counter. Then, a maximum of 255 Tx descriptors can be
>> added at once. In the current code the mvneta_txq_pend_desc_add function
>> assumes the caller takes care of this limit. But it is not the case. In
>> some situations (xmit_more flag), more than 255 descriptors are added.
>> When this happens, the Tx descriptor counter register is updated with a
>> wrong value, which breaks the whole Tx queue management.
>>
>> This patch fixes the issue by allowing the mvneta_txq_pend_desc_add
>> function to process more than 255 Tx descriptors.
>>
>> Fixes: 2a90f7e1d5d0 ("net: mvneta: add xmit_more support")
>> Cc: stable@vger.kernel.org # 4.11+
>> Signed-off-by: Simon Guinot <simon.guinot@sequanux.org>
>> ---
>>   drivers/net/ethernet/marvell/mvneta.c | 16 +++++++++-------
>>   1 file changed, 9 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
>> index 64a04975bcf8..027c08ce4e5d 100644
>> --- a/drivers/net/ethernet/marvell/mvneta.c
>> +++ b/drivers/net/ethernet/marvell/mvneta.c
>> @@ -816,11 +816,14 @@ static void mvneta_txq_pend_desc_add(struct mvneta_port *pp,
>>   {
>>   	u32 val;
>>   
>> -	/* Only 255 descriptors can be added at once ; Assume caller
>> -	 * process TX desriptors in quanta less than 256
>> -	 */
>> -	val = pend_desc + txq->pending;
>> -	mvreg_write(pp, MVNETA_TXQ_UPDATE_REG(txq->id), val);
>> +	pend_desc += txq->pending;
>> +
>> +	/* Only 255 Tx descriptors can be added at once */
>> +	while (pend_desc > 0) {
>> +		val = min(pend_desc, 255);
>> +		mvreg_write(pp, MVNETA_TXQ_UPDATE_REG(txq->id), val);
>> +		pend_desc -= val;
>> +	}
>>   	txq->pending = 0;
>>   }
>>   
>> @@ -2413,8 +2416,7 @@ static int mvneta_tx(struct sk_buff *skb, struct net_device *dev)
>>   		if (txq->count >= txq->tx_stop_threshold)
>>   			netif_tx_stop_queue(nq);
>>   
>> -		if (!skb->xmit_more || netif_xmit_stopped(nq) ||
>> -		    txq->pending + frags > MVNETA_TXQ_DEC_SENT_MASK)
>> +		if (!skb->xmit_more || netif_xmit_stopped(nq))
>>   			mvneta_txq_pend_desc_add(pp, txq, frags);
>>   		else
>>   			txq->pending += frags;
>> -- 
>> 2.9.3