Subject: Re: [PATCH 4/4] sctp: fix association hangs due to partial delivery errors

From: Vlad Yasevich <[email-masked]>
Date: Tue, 26 Feb 2013 21:34:56 -0500

On 02/26/2013 09:36 AM, Lee A. Roberts wrote:
> From: "Lee A. Roberts" <[email-masked]>
>
> Resolve SCTP association hangs observed during SCTP stress
> testing.  Observable symptoms include communications hangs
> with data being held in the association reassembly and/or lobby
> (ordering) queues.  Close examination of reassembly queue shows
> missing packets.
>
> In sctp_ulpq_tail_data(), use return values 0,1 to indicate whether
> a complete event (with MSG_EOR set) was delivered.  A return value
> of -ENOMEM continues to indicate an out-of-memory condition was
> encountered.
>
> In sctp_ulpq_retrieve_partial() and sctp_ulpq_retrieve_first(),
> correct message reassembly logic for SCTP partial delivery.
> Change logic to ensure that as much data as possible is sent
> with the initial partial delivery and that following partial
> deliveries contain all available data.
>
> In sctp_ulpq_partial_delivery(), attempt partial delivery only
> if the data on the head of the reassembly queue is at or before
> the cumulative TSN ACK point.
>
> In sctp_ulpq_renege(), use the modified return values from
> sctp_ulpq_tail_data() to choose whether to attempt partial
> delivery or to attempt to drain the reassembly queue as a
> means to reduce memory pressure.  Remove call to
> sctp_tsnmap_mark(), as this is handled correctly in call to
> sctp_ulpq_tail_data().
>
> Signed-off-by: Lee A. Roberts <[email-masked]>
> ---
>   net/sctp/ulpqueue.c |   54 ++++++++++++++++++++++++++++++++++++++++-----------
>   1 file changed, 43 insertions(+), 11 deletions(-)
>
> diff --git a/net/sctp/ulpqueue.c b/net/sctp/ulpqueue.c
> index f221fbb..482e3ea 100644
> --- a/net/sctp/ulpqueue.c
> +++ b/net/sctp/ulpqueue.c
> @@ -106,6 +106,7 @@ int sctp_ulpq_tail_data(struct sctp_ulpq *ulpq, struct sctp_chunk *chunk,
>   {
>   	struct sk_buff_head temp;
>   	struct sctp_ulpevent *event;
> +	int event_eor = 0;
>
>   	/* Create an event from the incoming chunk. */
>   	event = sctp_ulpevent_make_rcvmsg(chunk->asoc, chunk, gfp);
> @@ -127,10 +128,12 @@ int sctp_ulpq_tail_data(struct sctp_ulpq *ulpq, struct sctp_chunk *chunk,
>   	/* Send event to the ULP.  'event' is the sctp_ulpevent for
>   	 * very first SKB on the 'temp' list.
>   	 */
> -	if (event)
> +	if (event) {
> +		event_eor = (event->msg_flags & MSG_EOR) ? 1 : 0;
>   		sctp_ulpq_tail_event(ulpq, event);
> +	}

You can re-use the check just before this one to catch the EOR 
condition.   You already do
	if ((event) && (event->msg_flags & MSG_EOR)){

right after you try to get a reassembled event.

Everything else looks good.
-vlad

>
> -	return 0;
> +	return event_eor;
>   }
>
>   /* Add a new event for propagation to the ULP.  */
> @@ -540,14 +543,19 @@ static struct sctp_ulpevent *sctp_ulpq_retrieve_partial(struct sctp_ulpq *ulpq)
>   		ctsn = cevent->tsn;
>
>   		switch (cevent->msg_flags & SCTP_DATA_FRAG_MASK) {
> +		case SCTP_DATA_FIRST_FRAG:
> +			if (!first_frag)
> +				return NULL;
> +			goto done;
>   		case SCTP_DATA_MIDDLE_FRAG:
>   			if (!first_frag) {
>   				first_frag = pos;
>   				next_tsn = ctsn + 1;
>   				last_frag = pos;
> -			} else if (next_tsn == ctsn)
> +			} else if (next_tsn == ctsn) {
>   				next_tsn++;
> -			else
> +				last_frag = pos;
> +			} else
>   				goto done;
>   			break;
>   		case SCTP_DATA_LAST_FRAG:
> @@ -651,6 +659,14 @@ static struct sctp_ulpevent *sctp_ulpq_retrieve_first(struct sctp_ulpq *ulpq)
>   			} else
>   				goto done;
>   			break;
> +
> +		case SCTP_DATA_LAST_FRAG:
> +			if (!first_frag)
> +				return NULL;
> +			else
> +				goto done;
> +			break;
> +
>   		default:
>   			return NULL;
>   		}
> @@ -1025,16 +1041,28 @@ void sctp_ulpq_partial_delivery(struct sctp_ulpq *ulpq,
>   	struct sctp_ulpevent *event;
>   	struct sctp_association *asoc;
>   	struct sctp_sock *sp;
> +	__u32 ctsn;
> +	struct sk_buff *skb;
>
>   	asoc = ulpq->asoc;
>   	sp = sctp_sk(asoc->base.sk);
>
>   	/* If the association is already in Partial Delivery mode
> -	 * we have noting to do.
> +	 * we have nothing to do.
>   	 */
>   	if (ulpq->pd_mode)
>   		return;
>
> +	/* Data must be at or below the Cumulative TSN ACK Point to
> +	 * start partial delivery.
> +	 */
> +	skb = skb_peek(&asoc->ulpq.reasm);
> +	if (skb != NULL) {
> +		ctsn = sctp_skb2event(skb)->tsn;
> +		if (!TSN_lte(ctsn, sctp_tsnmap_get_ctsn(&asoc->peer.tsn_map)))
> +			return;
> +	}
> +
>   	/* If the user enabled fragment interleave socket option,
>   	 * multiple associations can enter partial delivery.
>   	 * Otherwise, we can only enter partial delivery if the
> @@ -1077,12 +1105,16 @@ void sctp_ulpq_renege(struct sctp_ulpq *ulpq, struct sctp_chunk *chunk,
>   	}
>   	/* If able to free enough room, accept this chunk. */
>   	if (chunk && (freed >= needed)) {
> -		__u32 tsn;
> -		tsn = ntohl(chunk->subh.data_hdr->tsn);
> -		sctp_tsnmap_mark(&asoc->peer.tsn_map, tsn, chunk->transport);
> -		sctp_ulpq_tail_data(ulpq, chunk, gfp);
> -
> -		sctp_ulpq_partial_delivery(ulpq, gfp);
> +		int retval;
> +		retval = sctp_ulpq_tail_data(ulpq, chunk, gfp);
> +		/*
> +		 * Enter partial delivery if chunk has not been
> +		 * delivered; otherwise, drain the reassembly queue.
> +		 */
> +		if (retval <= 0)
> +			sctp_ulpq_partial_delivery(ulpq, chunk, gfp);
> +		else if (retval == 1)
> +			sctp_ulpq_reasm_drain(ulpq);
>   	}
>
>   	sk_mem_reclaim(asoc->base.sk);
>