On Fri, Dec 23, 2016 at 02:29:02PM -0200, Marcelo Ricardo Leitner wrote:
> It's possible that we receive a packet that is larger than current
> window. If it's the first packet in this way, it will cause it to
> increase rwnd_over. Then, if we receive another data chunk (specially as
> SCTP allows you to have one data chunk in flight even during 0 window),
> rwnd_over will be overwritten instead of added to.
>
> In the long run, this could cause the window to grow bigger than its
> initial size, as rwnd_over would be charged only for the last received
> data chunk while the code will try open the window for all packets that
> were received and had its value in rwnd_over overwritten. This, then,
> can lead to the worsening of payload/buffer ratio and cause rwnd_press
> to kick in more often.
>
> The fix is to sum it too, same as is done for rwnd_press, so that if we
> receive 3 chunks after closing the window, we still have to release that
> same amount before re-opening it.
>
> Log snippet from sctp_test exhibiting the issue:
> [ 146.209232] sctp: sctp_assoc_rwnd_decrease: asoc:ffff88013928e000
> rwnd decreased by 1 to (0, 1, 114221)
> [ 146.209232] sctp: sctp_assoc_rwnd_decrease:
> association:ffff88013928e000 has asoc->rwnd:0, asoc->rwnd_over:1!
> [ 146.209232] sctp: sctp_assoc_rwnd_decrease: asoc:ffff88013928e000
> rwnd decreased by 1 to (0, 1, 114221)
> [ 146.209232] sctp: sctp_assoc_rwnd_decrease:
> association:ffff88013928e000 has asoc->rwnd:0, asoc->rwnd_over:1!
> [ 146.209232] sctp: sctp_assoc_rwnd_decrease: asoc:ffff88013928e000
> rwnd decreased by 1 to (0, 1, 114221)
> [ 146.209232] sctp: sctp_assoc_rwnd_decrease:
> association:ffff88013928e000 has asoc->rwnd:0, asoc->rwnd_over:1!
> [ 146.209232] sctp: sctp_assoc_rwnd_decrease: asoc:ffff88013928e000
> rwnd decreased by 1 to (0, 1, 114221)
>
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx>
> ---
> net/sctp/associola.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/sctp/associola.c b/net/sctp/associola.c
> index 68428e1f71810fbe65b7f86c750c3ad61f0266ec..56ddcfaeb4f64235b54b0daa915fabf0cc0170a9 100644
> --- a/net/sctp/associola.c
> +++ b/net/sctp/associola.c
> @@ -1539,7 +1539,7 @@ void sctp_assoc_rwnd_decrease(struct sctp_association *asoc, unsigned int len)
> asoc->rwnd = 0;
> }
> } else {
> - asoc->rwnd_over = len - asoc->rwnd;
> + asoc->rwnd_over += len - asoc->rwnd;
> asoc->rwnd = 0;
> }
>
> --
> 2.9.3
>
>
Acked-by: Neil Horman <nhorman@xxxxxxxxxxxxx>
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