netdev - Re: [PATCH 2/3] sctp_diag: export timer value only if it is active

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Date:	Sat, 30 Jul 2016 21:25:42 +0800
From:	Xin Long <lucien.xin@...il.com>
To:	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:	Phil Sutter <phil@....cc>, David Miller <davem@...emloft.net>,
	network dev <netdev@...r.kernel.org>
Subject: Re: [PATCH 2/3] sctp_diag: export timer value only if it is active

>> diff --git a/net/sctp/sctp_diag.c b/net/sctp/sctp_diag.c
>> index f69edcf219e51..0ad6033a7330c 100644
>> --- a/net/sctp/sctp_diag.c
>> +++ b/net/sctp/sctp_diag.c
>> @@ -40,10 +40,12 @@ static void inet_diag_msg_sctpasoc_fill(struct inet_diag_msg *r,
>>       }
>>
>>       r->idiag_state = asoc->state;
>> -     r->idiag_timer = SCTP_EVENT_TIMEOUT_T3_RTX;
>> -     r->idiag_retrans = asoc->rtx_data_chunks;
>> -     r->idiag_expires = jiffies_to_msecs(
>> -             asoc->timeouts[SCTP_EVENT_TIMEOUT_T3_RTX] - jiffies);
>
> I think we have two issues here, prior to your patch, but I noticed
> while reviewing it :-)
>
> This array is actually not based on jiffies but on intervals instead, as
> per:
>
> sm_sideeffect.c:
>                 case SCTP_CMD_TIMER_START:                       [1]
>                         timer = &asoc->timers[cmd->obj.to];
>                         timeout = asoc->timeouts[cmd->obj.to];   <---
>                         BUG_ON(!timeout);
>
>                         timer->expires = jiffies + timeout;      <---
understood.

>
> But more importantly, this array is actually not used for this timeout
> and the timeout is sctp_transport dependant, as per:
>
> /* Schedule retransmission on the given transport */
> void sctp_transport_immediate_rtx(struct sctp_transport *t)
> {
>         /* Stop pending T3_rtx_timer */
>         if (del_timer(&t->T3_rtx_timer))
>                 sctp_transport_put(t);
>
>         sctp_retransmit(&t->asoc->outqueue, t, SCTP_RTXR_T3_RTX);
>         if (!timer_pending(&t->T3_rtx_timer)) {
>                 if (!mod_timer(&t->T3_rtx_timer, jiffies + t->rto))
>                                                  ^^^^^^^^^^^^^^^^
>                         sctp_transport_hold(t);
>
> Note how on sctp_get_sctp_info() it fetches the RTO (which is T3_RTX)
> this way:
>         info->sctpi_p_rto = jiffies_to_msecs(prim->rto);
> If we want to know how long is left for the timer to expire, we have to
> read directly from it.
you are right, 3 timers (T3_tx, hb, rtx_data_chunks) are per transport.

>
> With git grep -A 1 TIMER_START we can confirm that [1] is never hit for
> SCTP_EVENT_TIMEOUT_T3_RTX. Yet, the asoc is allocated with kzalloc(), so
> I guess you were just reading -jiffies in there.
>
> Note however that the stats rtx_data_chunks is the accumulated stats,
> it's good, and that we may have multiple T3 timers running at once, with
> different timeouts.
>
> Xin, ideas on how we can fix this? I'm not sure if we can dump
> per-transport info in there. Not as it is now, I guess.
It's not that easy to dump all transports info besed on current sctp_diag codes.

Now for the transport's info,  we only choose primary_path to dump.
It means we should fix this by getting the left time to expire from
primary transport t->T3_rtx_timer. like:

        r->idiag_expires = jiffies_to_msecs(
-               asoc->timeouts[SCTP_EVENT_TIMEOUT_T3_RTX] - jiffies);
+               asoc->peer.primary_path->T3_rtx_timer.expires - jiffies);

but yes, need to check with timer_pending firstly.

what do  you think ?