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Date: Fri, 27 Dec 2019 19:42:39 +0800
From: Kevin Kou <qdkevin.kou@...il.com>
To: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc: linux-sctp@...r.kernel.org, netdev@...r.kernel.org,
nhorman@...driver.com, davem@...emloft.net
Subject: Re: [PATCHv2 net-next] sctp: move trace_sctp_probe_path into
sctp_outq_sack
On 2019/12/27 18:47, Marcelo Ricardo Leitner wrote:
> On Fri, Dec 27, 2019 at 08:00:34AM +0000, Kevin Kou wrote:
>> The original patch bringed in the "SCTP ACK tracking trace event"
>> feature was committed at Dec.20, 2017, it replaced jprobe usage
>> with trace events, and bringed in two trace events, one is
>> TRACE_EVENT(sctp_probe), another one is TRACE_EVENT(sctp_probe_path).
>> The original patch intended to trigger the trace_sctp_probe_path in
>> TRACE_EVENT(sctp_probe) as below code,
>>
>> +TRACE_EVENT(sctp_probe,
>> +
>> + TP_PROTO(const struct sctp_endpoint *ep,
>> + const struct sctp_association *asoc,
>> + struct sctp_chunk *chunk),
>> +
>> + TP_ARGS(ep, asoc, chunk),
>> +
>> + TP_STRUCT__entry(
>> + __field(__u64, asoc)
>> + __field(__u32, mark)
>> + __field(__u16, bind_port)
>> + __field(__u16, peer_port)
>> + __field(__u32, pathmtu)
>> + __field(__u32, rwnd)
>> + __field(__u16, unack_data)
>> + ),
>> +
>> + TP_fast_assign(
>> + struct sk_buff *skb = chunk->skb;
>> +
>> + __entry->asoc = (unsigned long)asoc;
>> + __entry->mark = skb->mark;
>> + __entry->bind_port = ep->base.bind_addr.port;
>> + __entry->peer_port = asoc->peer.port;
>> + __entry->pathmtu = asoc->pathmtu;
>> + __entry->rwnd = asoc->peer.rwnd;
>> + __entry->unack_data = asoc->unack_data;
>> +
>> + if (trace_sctp_probe_path_enabled()) {
>> + struct sctp_transport *sp;
>> +
>> + list_for_each_entry(sp, &asoc->peer.transport_addr_list,
>> + transports) {
>> + trace_sctp_probe_path(sp, asoc);
>> + }
>> + }
>> + ),
>>
>> But I found it did not work when I did testing, and trace_sctp_probe_path
>> had no output, I finally found that there is trace buffer lock
>> operation(trace_event_buffer_reserve) in include/trace/trace_events.h:
>>
>> static notrace void \
>> trace_event_raw_event_##call(void *__data, proto) \
>> { \
>> struct trace_event_file *trace_file = __data; \
>> struct trace_event_data_offsets_##call __maybe_unused __data_offsets;\
>> struct trace_event_buffer fbuffer; \
>> struct trace_event_raw_##call *entry; \
>> int __data_size; \
>> \
>> if (trace_trigger_soft_disabled(trace_file)) \
>> return; \
>> \
>> __data_size = trace_event_get_offsets_##call(&__data_offsets, args); \
>> \
>> entry = trace_event_buffer_reserve(&fbuffer, trace_file, \
>> sizeof(*entry) + __data_size); \
>> \
>> if (!entry) \
>> return; \
>> \
>> tstruct \
>> \
>> { assign; } \
>> \
>> trace_event_buffer_commit(&fbuffer); \
>> }
>>
>> The reason caused no output of trace_sctp_probe_path is that
>> trace_sctp_probe_path written in TP_fast_assign part of
>> TRACE_EVENT(sctp_probe), and it will be placed( { assign; } ) after the
>> trace_event_buffer_reserve() when compiler expands Macro,
>>
>> entry = trace_event_buffer_reserve(&fbuffer, trace_file, \
>> sizeof(*entry) + __data_size); \
>> \
>> if (!entry) \
>> return; \
>> \
>> tstruct \
>> \
>> { assign; } \
>>
>> so trace_sctp_probe_path finally can not acquire trace_event_buffer
>> and return no output, that is to say the nest of tracepoint entry function
>> is not allowed. The function call flow is:
>>
>> trace_sctp_probe()
>> -> trace_event_raw_event_sctp_probe()
>> -> lock buffer
>> -> trace_sctp_probe_path()
>> -> trace_event_raw_event_sctp_probe_path() --nested
>> -> buffer has been locked and return no output.
>>
>> This patch is to remove trace_sctp_probe_path from the TP_fast_assign
>> part of TRACE_EVENT(sctp_probe) to avoid the nest of entry function,
>> and trigger sctp_probe_path_trace in sctp_outq_sack.
>>
>> After this patch, you can enable both events individually,
>> # cd /sys/kernel/debug/tracing
>> # echo 1 > events/sctp/sctp_probe/enable
>> # echo 1 > events/sctp/sctp_probe_path/enable
>>
>> Or, you can enable all the events under sctp.
>>
>> # echo 1 > events/sctp/enable
>>
>> v1->v2:
>> -add trace_sctp_probe_path_enabled check to avoid traversing the
>> transport list when the tracepoint is disabled as Marcelo's suggestion.
>
> Oh, nice, thanks for taking the time to add it back.
>
> Dave already applied your v1, so you actually need an incremental
> patch now :-)
>
Thank you for your guidance, Marcelo. I will create the incremental
patch soon. :-)
>>
>> Signed-off-by: Kevin Kou <qdkevin.kou@...il.com>
>> ---
>> include/trace/events/sctp.h | 9 ---------
>> net/sctp/outqueue.c | 7 +++++++
>> 2 files changed, 7 insertions(+), 9 deletions(-)
>>
>> diff --git a/include/trace/events/sctp.h b/include/trace/events/sctp.h
>> index 7475c7b..d4aac34 100644
>> --- a/include/trace/events/sctp.h
>> +++ b/include/trace/events/sctp.h
>> @@ -75,15 +75,6 @@
>> __entry->pathmtu = asoc->pathmtu;
>> __entry->rwnd = asoc->peer.rwnd;
>> __entry->unack_data = asoc->unack_data;
>> -
>> - if (trace_sctp_probe_path_enabled()) {
>> - struct sctp_transport *sp;
>> -
>> - list_for_each_entry(sp, &asoc->peer.transport_addr_list,
>> - transports) {
>> - trace_sctp_probe_path(sp, asoc);
>> - }
>> - }
>> ),
>>
>> TP_printk("asoc=%#llx mark=%#x bind_port=%d peer_port=%d pathmtu=%d "
>> diff --git a/net/sctp/outqueue.c b/net/sctp/outqueue.c
>> index 0dab62b..83ddcfe 100644
>> --- a/net/sctp/outqueue.c
>> +++ b/net/sctp/outqueue.c
>> @@ -36,6 +36,7 @@
>> #include <net/sctp/sctp.h>
>> #include <net/sctp/sm.h>
>> #include <net/sctp/stream_sched.h>
>> +#include <trace/events/sctp.h>
>>
>> /* Declare internal functions here. */
>> static int sctp_acked(struct sctp_sackhdr *sack, __u32 tsn);
>> @@ -1238,6 +1239,12 @@ int sctp_outq_sack(struct sctp_outq *q, struct sctp_chunk *chunk)
>> /* Grab the association's destination address list. */
>> transport_list = &asoc->peer.transport_addr_list;
>>
>> + /* SCTP path tracepoint for congestion control debugging. */
>> + if (trace_sctp_probe_path_enabled()) {
>> + list_for_each_entry(transport, transport_list, transports)
>> + trace_sctp_probe_path(transport, asoc);
>> + }
>> +
>> sack_ctsn = ntohl(sack->cum_tsn_ack);
>> gap_ack_blocks = ntohs(sack->num_gap_ack_blocks);
>> asoc->stats.gapcnt += gap_ack_blocks;
>> --
>> 1.8.3.1
>>
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