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Date: Wed, 27 Feb 2013 08:51:04 -0500
From: Vlad Yasevich <vyasevic@...hat.com>
To: "Roberts, Lee A." <lee.roberts@...com>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 4/4] sctp: fix association hangs due to partial delivery
errors
On 02/26/2013 11:38 PM, Roberts, Lee A. wrote:
> Vlad,
>
>> -----Original Message-----
>> From: Vlad Yasevich [mailto:vyasevic@...hat.com]
>> Sent: Tuesday, February 26, 2013 7:35 PM
>> To: Roberts, Lee A.
>> Cc: netdev@...r.kernel.org
>> Subject: Re: [PATCH 4/4] sctp: fix association hangs due to partial delivery errors
>>
>> On 02/26/2013 09:36 AM, Lee A. Roberts wrote:
>>> From: "Lee A. Roberts" <lee.roberts@...com>
>>>
>>> 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 <lee.roberts@...com>
>>> ---
>>> 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
>>
> It depends on what we want the return value to mean. In the case where we've reneged
> to be able to put in a packet, we know that the incoming packet is the next one we're
> looking for. In which case, the earlier test is correct, since this will be the next
> event.
>
> In general, the event that's being passed to sctp_ulpq_order() might not be the
> next event. In that case, sctp_ulpq_order() will call sctp_ulpq_store_ordered()
> and return NULL. Only at the last "if (event)" can we really be sure that an event
> is being passed to the ULP.
>
> In general, do we want to return 1 if a complete event is actually passed to the ULP?
> Or, do we want to return 1 if we've seen a complete event come from reassembly?
You are right. We want it set based on deliver to ULP. There is a
probability (if PARTIAL_DELIVERY_POINT is set) that we might get
a partial message here without EOR and skip ordering. So, your check
is correct.
-vlad
>
> - Lee
>
>>>
>>> - 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);
>>>
>
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