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Date: Thu, 07 Jul 2011 09:36:26 -0400
From: Vladislav Yasevich <vladislav.yasevich@...com>
To: netdev@...r.kernel.org, davem@...emloft.net,
Wei Yongjun <yjwei@...fujitsu.com>,
Sridhar Samudrala <sri@...ibm.com>, linux-sctp@...r.kernel.org
Subject: Re: [PATCHv3] sctp: Enforce retransmission limit during shutdown
On 07/07/2011 06:28 AM, Thomas Graf wrote:
> When initiating a graceful shutdown while having data chunks
> on the retransmission queue with a peer which is in zero
> window mode the shutdown is never completed because the
> retransmission error count is reset periodically by the
> following two rules:
>
> - Do not timeout association while doing zero window probe.
> - Reset overall error count when a heartbeat request has
> been acknowledged.
>
> The graceful shutdown will wait for all outstanding TSN to
> be acknowledged before sending the SHUTDOWN request. This
> never happens due to the peer's zero window not acknowledging
> the continuously retransmitted data chunks. Although the
> error counter is incremented for each failed retransmission,
> the receiving of the SACK announcing the zero window clears
> the error count again immediately. Also heartbeat requests
> continue to be sent periodically. The peer acknowledges these
> requests causing the error counter to be reset as well.
>
> This patch changes behaviour to only reset the overall error
> counter for the above rules while not in shutdown. After
> reaching the maximum number of retransmission attempts, the
> T5 shutdown guard timer is scheduled to give the receiver
> some additional time to recover. The timer is stopped as soon
> as the receiver acknowledges any data.
>
> The issue can be easily reproduced by establishing a sctp
> association over the loopback device, constantly queueing
> data at the sender while not reading any at the receiver.
> Wait for the window to reach zero, then initiate a shutdown
> by killing both processes simultaneously. The association
> will never be freed and the chunks on the retransmission
> queue will be retransmitted indefinitely.
>
> Signed-off-by: Thomas Graf <tgraf@...radead.org>
Acked-by: Vlad Yasevich <vladislav.yasevich@...com>
Thanks
-vlad
>
> diff --git a/include/net/sctp/command.h b/include/net/sctp/command.h
> index dd6847e..6506458 100644
> --- a/include/net/sctp/command.h
> +++ b/include/net/sctp/command.h
> @@ -63,6 +63,7 @@ typedef enum {
> SCTP_CMD_ECN_ECNE, /* Do delayed ECNE processing. */
> SCTP_CMD_ECN_CWR, /* Do delayed CWR processing. */
> SCTP_CMD_TIMER_START, /* Start a timer. */
> + SCTP_CMD_TIMER_START_ONCE, /* Start a timer once */
> SCTP_CMD_TIMER_RESTART, /* Restart a timer. */
> SCTP_CMD_TIMER_STOP, /* Stop a timer. */
> SCTP_CMD_INIT_CHOOSE_TRANSPORT, /* Choose transport for an INIT. */
> diff --git a/net/sctp/outqueue.c b/net/sctp/outqueue.c
> index 1c88c89..d036821 100644
> --- a/net/sctp/outqueue.c
> +++ b/net/sctp/outqueue.c
> @@ -1582,6 +1582,8 @@ static void sctp_check_transmitted(struct sctp_outq *q,
> #endif /* SCTP_DEBUG */
> if (transport) {
> if (bytes_acked) {
> + struct sctp_association *asoc = transport->asoc;
> +
> /* We may have counted DATA that was migrated
> * to this transport due to DEL-IP operation.
> * Subtract those bytes, since the were never
> @@ -1600,6 +1602,17 @@ static void sctp_check_transmitted(struct sctp_outq *q,
> transport->error_count = 0;
> transport->asoc->overall_error_count = 0;
>
> + /*
> + * While in SHUTDOWN PENDING, we may have started
> + * the T5 shutdown guard timer after reaching the
> + * retransmission limit. Stop that timer as soon
> + * as the receiver acknowledged any data.
> + */
> + if (asoc->state == SCTP_STATE_SHUTDOWN_PENDING &&
> + del_timer(&asoc->timers
> + [SCTP_EVENT_TIMEOUT_T5_SHUTDOWN_GUARD]))
> + sctp_association_put(asoc);
> +
> /* Mark the destination transport address as
> * active if it is not so marked.
> */
> @@ -1629,10 +1642,15 @@ static void sctp_check_transmitted(struct sctp_outq *q,
> * A sender is doing zero window probing when the
> * receiver's advertised window is zero, and there is
> * only one data chunk in flight to the receiver.
> + *
> + * Allow the association to timeout while in SHUTDOWN
> + * PENDING or SHUTDOWN RECEIVED in case the receiver
> + * stays in zero window mode forever.
> */
> if (!q->asoc->peer.rwnd &&
> !list_empty(&tlist) &&
> - (sack_ctsn+2 == q->asoc->next_tsn)) {
> + (sack_ctsn+2 == q->asoc->next_tsn) &&
> + q->asoc->state < SCTP_STATE_SHUTDOWN_PENDING) {
> SCTP_DEBUG_PRINTK("%s: SACK received for zero "
> "window probe: %u\n",
> __func__, sack_ctsn);
> diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
> index 534c2e5..6e0f882 100644
> --- a/net/sctp/sm_sideeffect.c
> +++ b/net/sctp/sm_sideeffect.c
> @@ -670,10 +670,19 @@ static void sctp_cmd_transport_on(sctp_cmd_seq_t *cmds,
> /* 8.3 Upon the receipt of the HEARTBEAT ACK, the sender of the
> * HEARTBEAT should clear the error counter of the destination
> * transport address to which the HEARTBEAT was sent.
> - * The association's overall error count is also cleared.
> */
> t->error_count = 0;
> - t->asoc->overall_error_count = 0;
> +
> + /*
> + * Although RFC4960 specifies that the overall error count must
> + * be cleared when a HEARTBEAT ACK is received, we make an
> + * exception while in SHUTDOWN PENDING. If the peer keeps its
> + * window shut forever, we may never be able to transmit our
> + * outstanding data and rely on the retransmission limit be reached
> + * to shutdown the association.
> + */
> + if (t->asoc->state != SCTP_STATE_SHUTDOWN_PENDING)
> + t->asoc->overall_error_count = 0;
>
> /* Clear the hb_sent flag to signal that we had a good
> * acknowledgement.
> @@ -1437,6 +1446,13 @@ static int sctp_cmd_interpreter(sctp_event_t event_type,
> sctp_cmd_setup_t2(commands, asoc, cmd->obj.ptr);
> break;
>
> + case SCTP_CMD_TIMER_START_ONCE:
> + timer = &asoc->timers[cmd->obj.to];
> +
> + if (timer_pending(timer))
> + break;
> + /* fall through */
> +
> case SCTP_CMD_TIMER_START:
> timer = &asoc->timers[cmd->obj.to];
> timeout = asoc->timeouts[cmd->obj.to];
> diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
> index a297283..2461171 100644
> --- a/net/sctp/sm_statefuns.c
> +++ b/net/sctp/sm_statefuns.c
> @@ -5154,7 +5154,7 @@ sctp_disposition_t sctp_sf_do_9_2_start_shutdown(
> * The sender of the SHUTDOWN MAY also start an overall guard timer
> * 'T5-shutdown-guard' to bound the overall time for shutdown sequence.
> */
> - sctp_add_cmd_sf(commands, SCTP_CMD_TIMER_START,
> + sctp_add_cmd_sf(commands, SCTP_CMD_TIMER_RESTART,
> SCTP_TO(SCTP_EVENT_TIMEOUT_T5_SHUTDOWN_GUARD));
>
> if (asoc->autoclose)
> @@ -5299,14 +5299,28 @@ sctp_disposition_t sctp_sf_do_6_3_3_rtx(const struct sctp_endpoint *ep,
> SCTP_INC_STATS(SCTP_MIB_T3_RTX_EXPIREDS);
>
> if (asoc->overall_error_count >= asoc->max_retrans) {
> - sctp_add_cmd_sf(commands, SCTP_CMD_SET_SK_ERR,
> - SCTP_ERROR(ETIMEDOUT));
> - /* CMD_ASSOC_FAILED calls CMD_DELETE_TCB. */
> - sctp_add_cmd_sf(commands, SCTP_CMD_ASSOC_FAILED,
> - SCTP_PERR(SCTP_ERROR_NO_ERROR));
> - SCTP_INC_STATS(SCTP_MIB_ABORTEDS);
> - SCTP_DEC_STATS(SCTP_MIB_CURRESTAB);
> - return SCTP_DISPOSITION_DELETE_TCB;
> + if (asoc->state == SCTP_STATE_SHUTDOWN_PENDING) {
> + /*
> + * We are here likely because the receiver had its rwnd
> + * closed for a while and we have not been able to
> + * transmit the locally queued data within the maximum
> + * retransmission attempts limit. Start the T5
> + * shutdown guard timer to give the receiver one last
> + * chance and some additional time to recover before
> + * aborting.
> + */
> + sctp_add_cmd_sf(commands, SCTP_CMD_TIMER_START_ONCE,
> + SCTP_TO(SCTP_EVENT_TIMEOUT_T5_SHUTDOWN_GUARD));
> + } else {
> + sctp_add_cmd_sf(commands, SCTP_CMD_SET_SK_ERR,
> + SCTP_ERROR(ETIMEDOUT));
> + /* CMD_ASSOC_FAILED calls CMD_DELETE_TCB. */
> + sctp_add_cmd_sf(commands, SCTP_CMD_ASSOC_FAILED,
> + SCTP_PERR(SCTP_ERROR_NO_ERROR));
> + SCTP_INC_STATS(SCTP_MIB_ABORTEDS);
> + SCTP_DEC_STATS(SCTP_MIB_CURRESTAB);
> + return SCTP_DISPOSITION_DELETE_TCB;
> + }
> }
>
> /* E1) For the destination address for which the timer
> diff --git a/net/sctp/sm_statetable.c b/net/sctp/sm_statetable.c
> index 0338dc6..7c211a7 100644
> --- a/net/sctp/sm_statetable.c
> +++ b/net/sctp/sm_statetable.c
> @@ -827,7 +827,7 @@ static const sctp_sm_table_entry_t other_event_table[SCTP_NUM_OTHER_TYPES][SCTP_
> /* SCTP_STATE_ESTABLISHED */ \
> TYPE_SCTP_FUNC(sctp_sf_timer_ignore), \
> /* SCTP_STATE_SHUTDOWN_PENDING */ \
> - TYPE_SCTP_FUNC(sctp_sf_timer_ignore), \
> + TYPE_SCTP_FUNC(sctp_sf_t5_timer_expire), \
> /* SCTP_STATE_SHUTDOWN_SENT */ \
> TYPE_SCTP_FUNC(sctp_sf_t5_timer_expire), \
> /* SCTP_STATE_SHUTDOWN_RECEIVED */ \
>
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