Re: [PATCH] sctp: do trace_sctp_probe after SACK validation and check

[kevin kou]

As this trace used to trace the changes of SCTP association state in response to incoming packets(SACK). It is used for debugging SCTP congestion control algorithms, so according to the code in include/trace/events/sctp.h, this trace event only prints the below information, and seems it is hard to point out if the SACK is duplicate one.Â



TP_printk("asoc=%#llx%s ipaddr=%pISpc state=%u cwnd=%u ssthresh=%u " "flight_size=%u partial_bytes_acked=%u pathmtu=%u", __entry->asoc, __entry->primary ? "(*)" : "", __entry->ipaddr, __entry->state, __entry->cwnd, __entry->ssthresh, __entry->flight_size, __entry->partial_bytes_acked, __entry->pathmtu)


2019å12æ21æ 00:18, 00:18ïå Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx> åå:
>On Fri, Dec 20, 2019 at 04:47:03AM +0000, Kevin Kou wrote:
>> The function sctp_sf_eat_sack_6_2 now performs
>> the Verification Tag validation, Chunk length validation, Bogu check,
>> and also the detection of out-of-order SACK based on the RFC2960
>> Section 6.2 at the beginning, and finally performs the further
>> processing of SACK. The trace_sctp_probe now triggered before
>> the above necessary validation and check.
>>
>> This patch is to do the trace_sctp_probe after the necessary check
>> and validation to SACK.
>>
>> Signed-off-by: Kevin Kou <qdkevin.kou@xxxxxxxxx>
>> ---
>>  net/sctp/sm_statefuns.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
>> index 42558fa..b4a54df 100644
>> --- a/net/sctp/sm_statefuns.c
>> +++ b/net/sctp/sm_statefuns.c
>> @@ -3281,7 +3281,6 @@ enum sctp_disposition
>sctp_sf_eat_sack_6_2(struct net *net,
>>  	struct sctp_sackhdr *sackh;
>>  	__u32 ctsn;
>>
>> -	trace_sctp_probe(ep, asoc, chunk);
>>
>>  	if (!sctp_vtag_verify(chunk, asoc))
>>  		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
>> @@ -3319,6 +3318,8 @@ enum sctp_disposition
>sctp_sf_eat_sack_6_2(struct net *net,
>>  	if (!TSN_lt(ctsn, asoc->next_tsn))
>>  		return sctp_sf_violation_ctsn(net, ep, asoc, type, arg, commands);
>>
>> +	trace_sctp_probe(ep, asoc, chunk);
>> +
>
>Moving it here will be after the check against ctsn_ack_point, which
>could cause duplicated SACKs to be missed from the log.
>
>Yes, from the sender-side CC we don't care about it (yet), but it
>helps to spot probably avoidable retransmissions.
>
>I think this is cleaning up the noise too much. I can agree with
>moving it to after the chunk sanity tests, though.
>
>>  	/* Return this SACK for further processing.  */
>>  	sctp_add_cmd_sf(commands, SCTP_CMD_PROCESS_SACK,
>SCTP_CHUNK(chunk));
>>
>> --
>> 1.8.3.1
>>