Re: [PATCH net] sctp: use the pmtu from the icmp packet to update transport pathmtu

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

On Mon, Oct 15, 2018 at 07:58:29PM +0800, Xin Long wrote:
> Other than asoc pmtu sync from all transports, sctp_assoc_sync_pmtu
> is also processing transport pmtu_pending by icmp packets. But it's
> meaningless to use sctp_dst_mtu(t->dst) as new pmtu for a transport.
> 
> The right pmtu value should come from the icmp packet, and it would
> be saved into transport->mtu_info in this patch and used later when
> the pmtu sync happens in sctp_sendmsg_to_asoc or sctp_packet_config.
> 
> Besides, without this patch, as pmtu can only be updated correctly
> when receiving a icmp packet and no place is holding sock lock, it
> will take long time if the sock is busy with sending packets.
> 
> Note that it doesn't process transport->mtu_info in .release_cb(),
> as there is no enough information for pmtu update, like for which
> asoc or transport. It is not worth traversing all asocs to check
> pmtu_pending. So unlike tcp, sctp does this in tx path, for which
> mtu_info needs to be atomic_t.
> 
> Signed-off-by: Xin Long <lucien.xin@gmail.com>

Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>

> ---
>  include/net/sctp/structs.h | 2 ++
>  net/sctp/associola.c       | 3 ++-
>  net/sctp/input.c           | 1 +
>  net/sctp/output.c          | 6 ++++++
>  4 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
> index 28a7c8e..a11f937 100644
> --- a/include/net/sctp/structs.h
> +++ b/include/net/sctp/structs.h
> @@ -876,6 +876,8 @@ struct sctp_transport {
>  	unsigned long sackdelay;
>  	__u32 sackfreq;
>  
> +	atomic_t mtu_info;
> +
>  	/* When was the last time that we heard from this transport? We use
>  	 * this to pick new active and retran paths.
>  	 */
> diff --git a/net/sctp/associola.c b/net/sctp/associola.c
> index 297d9cf..a827a1f 100644
> --- a/net/sctp/associola.c
> +++ b/net/sctp/associola.c
> @@ -1450,7 +1450,8 @@ void sctp_assoc_sync_pmtu(struct sctp_association *asoc)
>  	/* Get the lowest pmtu of all the transports. */
>  	list_for_each_entry(t, &asoc->peer.transport_addr_list, transports) {
>  		if (t->pmtu_pending && t->dst) {
> -			sctp_transport_update_pmtu(t, sctp_dst_mtu(t->dst));
> +			sctp_transport_update_pmtu(t,
> +						   atomic_read(&t->mtu_info));
>  			t->pmtu_pending = 0;
>  		}
>  		if (!pmtu || (t->pathmtu < pmtu))
> diff --git a/net/sctp/input.c b/net/sctp/input.c
> index 9bbc5f9..5c36a99 100644
> --- a/net/sctp/input.c
> +++ b/net/sctp/input.c
> @@ -395,6 +395,7 @@ void sctp_icmp_frag_needed(struct sock *sk, struct sctp_association *asoc,
>  		return;
>  
>  	if (sock_owned_by_user(sk)) {
> +		atomic_set(&t->mtu_info, pmtu);
>  		asoc->pmtu_pending = 1;
>  		t->pmtu_pending = 1;
>  		return;
> diff --git a/net/sctp/output.c b/net/sctp/output.c
> index 7f849b0..67939ad 100644
> --- a/net/sctp/output.c
> +++ b/net/sctp/output.c
> @@ -120,6 +120,12 @@ void sctp_packet_config(struct sctp_packet *packet, __u32 vtag,
>  			sctp_assoc_sync_pmtu(asoc);
>  	}
>  
> +	if (asoc->pmtu_pending) {
> +		if (asoc->param_flags & SPP_PMTUD_ENABLE)
> +			sctp_assoc_sync_pmtu(asoc);
> +		asoc->pmtu_pending = 0;
> +	}
> +
>  	/* If there a is a prepend chunk stick it on the list before
>  	 * any other chunks get appended.
>  	 */
> -- 
> 2.1.0
>