Subject: Re: [PATCHv2 net] sctp: change to save MSG_MORE flag into assoc

From: Marcelo Ricardo Leitner <[email-masked]>
Date: Tue, 28 Mar 2017 15:04:54 -0300

On Tue, Mar 28, 2017 at 12:17:00PM +0800, Xin Long wrote:
> On Tue, Mar 28, 2017 at 6:43 AM, Marcelo Ricardo Leitner
> <[email-masked]> 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 <[email-masked]>
> >> ---
> >>  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;

Ah yes, okay.

Acked-by: Marcelo Ricardo Leitner <[email-masked]>

> 
> 
> 
> >
> > 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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