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

[Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>]

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@gmail.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.

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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