Subject: Re: [PATCH net] sctp: check for dst and pathmtu update in sctp_packet_config

From: Marcelo Ricardo Leitner <[email-masked]>
Date: Sat, 1 Apr 2017 10:35:32 -0300

On Sat, Apr 01, 2017 at 05:15:59PM +0800, Xin Long wrote:
> This patch is to move sctp_transport_dst_check into sctp_packet_config
> from sctp_packet_transmit and add pathmtu check in sctp_packet_config.
> 
> With this fix, sctp can update dst or pathmtu before appending chunks,
> which can void dropping packets in sctp_packet_transmit when dst is
> obsolete or dst's mtu is changed.
> 
> This patch is also to improve some other codes in sctp_packet_config.
> It updates packet max_size with gso_max_size, checks for dst and
> pathmtu, and appends ecne chunk only when packet is empty and asoc
> is not NULL.
> 
> It makes sctp flush work better, as we only need to set up them once
> for one flush schedule. It's also safe, since asoc is NULL only when
> the packet is created by sctp_ootb_pkt_new in which it just gets the
> new dst, no need to do more things for it other than set packet with
> transport's pathmtu.
> 
> Signed-off-by: Xin Long <[email-masked]>

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

Thanks Xin.

> ---
>  include/net/sctp/sctp.h | 17 ++++++++++---
>  net/sctp/output.c       | 67 ++++++++++++++++++++++++++-----------------------
>  2 files changed, 50 insertions(+), 34 deletions(-)
> 
> diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
> index 1f71ee5..d75caa7 100644
> --- a/include/net/sctp/sctp.h
> +++ b/include/net/sctp/sctp.h
> @@ -596,12 +596,23 @@ static inline void sctp_v4_map_v6(union sctp_addr *addr)
>   */
>  static inline struct dst_entry *sctp_transport_dst_check(struct sctp_transport *t)
>  {
> -	if (t->dst && (!dst_check(t->dst, t->dst_cookie) ||
> -		       t->pathmtu != max_t(size_t, SCTP_TRUNC4(dst_mtu(t->dst)),
> -					   SCTP_DEFAULT_MINSEGMENT)))
> +	if (t->dst && !dst_check(t->dst, t->dst_cookie))
>  		sctp_transport_dst_release(t);
>  
>  	return t->dst;
>  }
>  
> +static inline bool sctp_transport_pmtu_check(struct sctp_transport *t)
> +{
> +	__u32 pmtu = max_t(size_t, SCTP_TRUNC4(dst_mtu(t->dst)),
> +			   SCTP_DEFAULT_MINSEGMENT);
> +
> +	if (t->pathmtu == pmtu)
> +		return true;
> +
> +	t->pathmtu = pmtu;
> +
> +	return false;
> +}
> +
>  #endif /* __net_sctp_h__ */
> diff --git a/net/sctp/output.c b/net/sctp/output.c
> index 73fd178..ec4d50a 100644
> --- a/net/sctp/output.c
> +++ b/net/sctp/output.c
> @@ -86,43 +86,53 @@ void sctp_packet_config(struct sctp_packet *packet, __u32 vtag,
>  {
>  	struct sctp_transport *tp = packet->transport;
>  	struct sctp_association *asoc = tp->asoc;
> +	struct sock *sk;
>  
>  	pr_debug("%s: packet:%p vtag:0x%x\n", __func__, packet, vtag);
> -
>  	packet->vtag = vtag;
>  
> -	if (asoc && tp->dst) {
> -		struct sock *sk = asoc->base.sk;
> -
> -		rcu_read_lock();
> -		if (__sk_dst_get(sk) != tp->dst) {
> -			dst_hold(tp->dst);
> -			sk_setup_caps(sk, tp->dst);
> -		}
> -
> -		if (sk_can_gso(sk)) {
> -			struct net_device *dev = tp->dst->dev;
> +	/* do the following jobs only once for a flush schedule */
> +	if (!sctp_packet_empty(packet))
> +		return;
>  
> -			packet->max_size = dev->gso_max_size;
> -		} else {
> -			packet->max_size = asoc->pathmtu;
> -		}
> -		rcu_read_unlock();
> +	/* set packet max_size with pathmtu */
> +	packet->max_size = tp->pathmtu;
> +	if (!asoc)
> +		return;
>  
> -	} else {
> -		packet->max_size = tp->pathmtu;
> +	/* update dst or transport pathmtu if in need */
> +	sk = asoc->base.sk;
> +	if (!sctp_transport_dst_check(tp)) {
> +		sctp_transport_route(tp, NULL, sctp_sk(sk));
> +		if (asoc->param_flags & SPP_PMTUD_ENABLE)
> +			sctp_assoc_sync_pmtu(sk, asoc);
> +	} else if (!sctp_transport_pmtu_check(tp)) {
> +		if (asoc->param_flags & SPP_PMTUD_ENABLE)
> +			sctp_assoc_sync_pmtu(sk, asoc);
>  	}
>  
> -	if (ecn_capable && sctp_packet_empty(packet)) {
> -		struct sctp_chunk *chunk;
> +	/* If there a is a prepend chunk stick it on the list before
> +	 * any other chunks get appended.
> +	 */
> +	if (ecn_capable) {
> +		struct sctp_chunk *chunk = sctp_get_ecne_prepend(asoc);
>  
> -		/* If there a is a prepend chunk stick it on the list before
> -		 * any other chunks get appended.
> -		 */
> -		chunk = sctp_get_ecne_prepend(asoc);
>  		if (chunk)
>  			sctp_packet_append_chunk(packet, chunk);
>  	}
> +
> +	if (!tp->dst)
> +		return;
> +
> +	/* set packet max_size with gso_max_size if gso is enabled*/
> +	rcu_read_lock();
> +	if (__sk_dst_get(sk) != tp->dst) {
> +		dst_hold(tp->dst);
> +		sk_setup_caps(sk, tp->dst);
> +	}
> +	packet->max_size = sk_can_gso(sk) ? tp->dst->dev->gso_max_size
> +					  : asoc->pathmtu;
> +	rcu_read_unlock();
>  }
>  
>  /* Initialize the packet structure. */
> @@ -582,12 +592,7 @@ int sctp_packet_transmit(struct sctp_packet *packet, gfp_t gfp)
>  	sh->vtag = htonl(packet->vtag);
>  	sh->checksum = 0;
>  
> -	/* update dst if in need */
> -	if (!sctp_transport_dst_check(tp)) {
> -		sctp_transport_route(tp, NULL, sctp_sk(sk));
> -		if (asoc && asoc->param_flags & SPP_PMTUD_ENABLE)
> -			sctp_assoc_sync_pmtu(sk, asoc);
> -	}
> +	/* drop packet if no dst */
>  	dst = dst_clone(tp->dst);
>  	if (!dst) {
>  		IP_INC_STATS(sock_net(sk), IPSTATS_MIB_OUTNOROUTES);
> -- 
> 2.1.0
> 
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