netdev - Re: [PATCH net] net: stmmac: fix completely hung TX when using TSO

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Date:   Tue, 6 Jun 2017 11:10:23 +0200
From:   Alexandre Torgue <alexandre.torgue@...com>
To:     Giuseppe CAVALLARO <peppe.cavallaro@...com>,
        Niklas Cassel <niklas.cassel@...s.com>
CC:     Niklas Cassel <niklass@...s.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] net: stmmac: fix completely hung TX when using TSO

Hi Guys,

On 06/06/2017 10:00 AM, Giuseppe CAVALLARO wrote:
> Hi Niklas
>
> I get the point and I acked the patch but Alex, please, can you confirm
> that this issue has never seen on your boxes where the TSO has been
> fully tested? The initial development (commit f748be531) introduces
> the following:
>     (last_segment) && (buff_size < TSO_MAX_BUFF_SIZE),

I don't remember to have seen this kind of issue in the past but for 
sure I agree with this patch.

Acked-by: Alexandre TORGUE <alexandre.torgue@...com>

> ...
>
> On 6/6/2017 9:25 AM, Niklas Cassel wrote:
>> stmmac_tso_allocator can fail to set the Last Descriptor bit
>> on a descriptor that actually was the last descriptor.
>>
>> This happens when the buffer of the last descriptor ends
>> up having a size of exactly TSO_MAX_BUFF_SIZE.
>>
>> When the IP eventually reaches the next last descriptor,
>> which actually has the bit set, the DMA will hang.
>>
>> When the DMA hangs, we get a tx timeout, however,
>> since stmmac does not do a complete reset of the IP
>> in stmmac_tx_timeout, we end up in a state with
>> completely hung TX.
>>
>> Signed-off-by: Niklas Cassel <niklas.cassel@...s.com>
>
> Acked-by: Giuseppe Cavallaro <peppe.cavallaro@...com>
>
>> ---
>>   drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> index 68a188e74c54..440bea049a7f 100644
>> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> @@ -2723,7 +2723,7 @@ static void stmmac_tso_allocator(struct
>> stmmac_priv *priv, unsigned int des,
>>             priv->hw->desc->prepare_tso_tx_desc(desc, 0, buff_size,
>>               0, 1,
>> -            (last_segment) && (buff_size < TSO_MAX_BUFF_SIZE),
>> +            (last_segment) && (tmp_len <= TSO_MAX_BUFF_SIZE),
>>               0, 0);
>>             tmp_len -= TSO_MAX_BUFF_SIZE;
>
> Regards
> Peppe
>
>