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Date:   Tue, 28 Mar 2017 12:17:00 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
        davem <davem@...emloft.net>, Neil Horman <nhorman@...driver.com>,
        David Laight <david.laight@...lab.com>
Subject: Re: [PATCHv2 net] sctp: change to save MSG_MORE flag into assoc

On Tue, Mar 28, 2017 at 6:43 AM, Marcelo Ricardo Leitner
<marcelo.leitner@...il.com> wrote:
> On Mon, Mar 27, 2017 at 12:21:15AM +0800, Xin Long wrote:
>> David Laight noticed the support for MSG_MORE with datamsg->force_delay
>> didn't really work as we expected, as the first msg with MSG_MORE set
>> would always block the following chunks' dequeuing.
>>
>> This Patch is to rewrite it by saving the MSG_MORE flag into assoc as
>> David Laight suggested.
>>
>> asoc->force_delay is used to save MSG_MORE flag before a msg is sent.
>> All chunks in queue would not be sent out if asoc->force_delay is set
>> by the msg with MSG_MORE flag, until a new msg without MSG_MORE flag
>> clears asoc->force_delay.
>>
>> Note that this change would not affect the flush is generated by other
>> triggers, like asoc->state != ESTABLISHED, queue size > pmtu etc.
>>
>> v1->v2:
>>   Not clear asoc->force_delay after sending the msg with MSG_MORE flag.
>>
>> Fixes: 4ea0c32f5f42 ("sctp: add support for MSG_MORE")
>> Signed-off-by: Xin Long <lucien.xin@...il.com>
>> ---
>>  include/net/sctp/structs.h | 2 +-
>>  net/sctp/output.c          | 2 +-
>>  net/sctp/socket.c          | 2 +-
>>  3 files changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
>> index 592dece..8caa5ee 100644
>> --- a/include/net/sctp/structs.h
>> +++ b/include/net/sctp/structs.h
>> @@ -499,7 +499,6 @@ struct sctp_datamsg {
>>       /* Did the messenge fail to send? */
>>       int send_error;
>>       u8 send_failed:1,
>> -        force_delay:1,
>>          can_delay;       /* should this message be Nagle delayed */
>>  };
>>
>> @@ -1878,6 +1877,7 @@ struct sctp_association {
>>
>>       __u8 need_ecne:1,       /* Need to send an ECNE Chunk? */
>>            temp:1,            /* Is it a temporary association? */
>> +          force_delay:1,
>>            prsctp_enable:1,
>>            reconf_enable:1;
>>
>> diff --git a/net/sctp/output.c b/net/sctp/output.c
>> index 1224421..73fd178 100644
>> --- a/net/sctp/output.c
>> +++ b/net/sctp/output.c
>> @@ -704,7 +704,7 @@ static sctp_xmit_t sctp_packet_can_append_data(struct sctp_packet *packet,
>>        */
>>
>>       if ((sctp_sk(asoc->base.sk)->nodelay || inflight == 0) &&
>> -         !chunk->msg->force_delay)
>> +         !asoc->force_delay)
>
> How is this going to not block the flush on asoc->state != ESTABLISHED?
> AFAICT b7018d0b6300 ("sctp: flush out queue once assoc state falls into
> SHUTDOWN_PENDING") need to clear asoc->force_delay too.

It won't block  the flush on asoc->state != ESTABLISHED,
in sctp_packet_can_append_data [1].

        if ((sctp_sk(asoc->base.sk)->nodelay || inflight == 0) &&
            !chunk->msg->force_delay)
                /* Nothing unacked */
                return SCTP_XMIT_OK;

        if (!sctp_packet_empty(packet))
                /* Append to packet */
                return SCTP_XMIT_OK;

        if (!sctp_state(asoc, ESTABLISHED)) <-----[1]
                return SCTP_XMIT_OK;



>
> Case I have in mind is the same old one:
> - app send a msg with MSG_MORE
> - close the asoc, without sending the final msg
>
>>               /* Nothing unacked */
>>               return SCTP_XMIT_OK;
>>
>> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
>> index 0f378ea..baa269a 100644
>> --- a/net/sctp/socket.c
>> +++ b/net/sctp/socket.c
>> @@ -1965,7 +1965,7 @@ static int sctp_sendmsg(struct sock *sk, struct msghdr *msg, size_t msg_len)
>>               err = PTR_ERR(datamsg);
>>               goto out_free;
>>       }
>> -     datamsg->force_delay = !!(msg->msg_flags & MSG_MORE);
>> +     asoc->force_delay = !!(msg->msg_flags & MSG_MORE);
>>
>>       /* Now send the (possibly) fragmented message. */
>>       list_for_each_entry(chunk, &datamsg->chunks, frag_list) {
>> --
>> 2.1.0
>>
>> --
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>>

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