net: sched: tbf: handle GSO_BY_FRAGS case in enqueue

tbf_enqueue() checks the size of a packet before enqueuing it.
However, the GSO size check does not consider the GSO_BY_FRAGS
case, and so will drop GSO SCTP packets, causing a massive drop
in throughput.

Use skb_gso_validate_mac_len() instead, as it does consider that
case.

---

skb_gso_validate_mac_len() is an out-of-line call, but so is
skb_gso_mac_seglen(), so this is slower but not much slower. I
will send a patch to make the skb_gso_validate_* functions
inline-able shortly.

Also, GSO_BY_FRAGS considered harmful - I'm pretty sure this is
not the only place it causes issues.

Signed-off-by: Daniel Axtens <dja@axtens.net>
---
 net/sched/sch_tbf.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

On Mon, Feb 05, 2018 at 02:34:33PM +1100, Daniel Axtens wrote:
> tbf_enqueue() checks the size of a packet before enqueuing it.
> However, the GSO size check does not consider the GSO_BY_FRAGS
> case, and so will drop GSO SCTP packets, causing a massive drop
> in throughput.
> 
> Use skb_gso_validate_mac_len() instead, as it does consider that
> case.
> 
> ---
> 
> skb_gso_validate_mac_len() is an out-of-line call, but so is
> skb_gso_mac_seglen(), so this is slower but not much slower. I
> will send a patch to make the skb_gso_validate_* functions
> inline-able shortly.
> 
> Also, GSO_BY_FRAGS considered harmful - I'm pretty sure this is
> not the only place it causes issues.

Thanks for spotting these issues and fixing them.

> 
> Signed-off-by: Daniel Axtens <dja@axtens.net>

If this block was meant to be an out-of-band/changelog comment, your
SOB line should be above the first --- marker.
Anyhow,
Reviewed-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>

> ---
>  net/sched/sch_tbf.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/net/sched/sch_tbf.c b/net/sched/sch_tbf.c
> index 229172d509cc..03225a8df973 100644
> --- a/net/sched/sch_tbf.c
> +++ b/net/sched/sch_tbf.c
> @@ -188,7 +188,8 @@ static int tbf_enqueue(struct sk_buff *skb, struct Qdisc *sch,
>  	int ret;
>  
>  	if (qdisc_pkt_len(skb) > q->max_size) {
> -		if (skb_is_gso(skb) && skb_gso_mac_seglen(skb) <= q->max_size)
> +		if (skb_is_gso(skb) &&
> +		    skb_gso_validate_mac_len(skb, q->max_size))
>  			return tbf_segment(skb, sch, to_free);
>  		return qdisc_drop(skb, sch, to_free);
>  	}
> -- 
> 2.14.1
>

Hi Marcelo,

>
> If this block was meant to be an out-of-band/changelog comment, your
> SOB line should be above the first --- marker.
> Anyhow,
> Reviewed-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>

Thanks - I did a v2 with this around the right way [1], but DaveM asked
me to be a bit more thorough and look for other GSO_BY_FRAGS issues. [2]

I did find a couple, including the one I asked you about with
qdisk_pkt_len_init [3] (thanks for your answer, btw). Currently I'm
trying to wrap my head around GSO_DODGY as Eric mentioned on that
thread, and then I'll do a series with this fix and the other
GSO_BY_FRAGS fixes I find.

Regards,
Daniel

[1] https://patchwork.ozlabs.org/patch/869145/
[2] https://patchwork.ozlabs.org/comment/1852414/
[3] https://www.spinics.net/lists/netdev/msg482397.html
>
>> ---
>>  net/sched/sch_tbf.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>> 
>> diff --git a/net/sched/sch_tbf.c b/net/sched/sch_tbf.c
>> index 229172d509cc..03225a8df973 100644
>> --- a/net/sched/sch_tbf.c
>> +++ b/net/sched/sch_tbf.c
>> @@ -188,7 +188,8 @@ static int tbf_enqueue(struct sk_buff *skb, struct Qdisc *sch,
>>  	int ret;
>>  
>>  	if (qdisc_pkt_len(skb) > q->max_size) {
>> -		if (skb_is_gso(skb) && skb_gso_mac_seglen(skb) <= q->max_size)
>> +		if (skb_is_gso(skb) &&
>> +		    skb_gso_validate_mac_len(skb, q->max_size))
>>  			return tbf_segment(skb, sch, to_free);
>>  		return qdisc_drop(skb, sch, to_free);
>>  	}
>> -- 
>> 2.14.1
>>