On 22/02/2019 09:45, kwiecienmaciek@xxxxxxxxx wrote:
> From: Maciej Kwiecien <maciej.kwiecien@xxxxxxxxx>
>
> hb_timer might not start at all for a particular transport because its
> start is conditional. In a result a node is not sending heartbeats.
>
> Function sctp_transport_reset_hb_timer has two roles:
> - initial start of hb_timer for a given transport,
> - update expire date of hb_timer for a given transport.
> The function is optimized to update timer's expire only if it is before
> a new calculated one but this comparison is invalid for a timer which
> has not yet started. Such a timer has expire == 0 and if a new expire
> value is bigger than (MAX_JIFFIES / 2 + 2) then "time_before" macro will
> fail and timer will not start resulting in no heartbeat packets send by
> the node.
>
> This was found when association was initialized within first 5 mins
> after system boot due to jiffies init value which is near to MAX_JIFFIES.
>
> Test kernel version: 4.9.154 (ARCH=arm)
> hb_timer.expire = 0; //initialized, not started timer
> new_expire = MAX_JIFFIES / 2 + 2; //or more
> time_before(hb_timer.expire, new_expire) == false
>
> Fixes: ba6f5e33bdbb ("sctp: avoid refreshing heartbeat timer too often")
> Reported-by: Marcin Stojek <marcin.stojek@xxxxxxxxx>
> Tested-by: Marcin Stojek <marcin.stojek@xxxxxxxxx>
Reviewed-by: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxx>
> Signed-off-by: Maciej Kwiecien <maciej.kwiecien@xxxxxxxxx>
> ---
> net/sctp/transport.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/sctp/transport.c b/net/sctp/transport.c
> index 033696e6f74f..ad158d311ffa 100644
> --- a/net/sctp/transport.c
> +++ b/net/sctp/transport.c
> @@ -207,7 +207,8 @@ void sctp_transport_reset_hb_timer(struct sctp_transport *transport)
>
> /* When a data chunk is sent, reset the heartbeat interval. */
> expires = jiffies + sctp_transport_timeout(transport);
> - if (time_before(transport->hb_timer.expires, expires) &&
> + if ((time_before(transport->hb_timer.expires, expires) ||
> + !timer_pending(&transport->hb_timer)) &&
> !mod_timer(&transport->hb_timer,
> expires + prandom_u32_max(transport->rto)))
> sctp_transport_hold(transport);
--
Best regards,
Alexander Sverdlin.
