Re: [PATCH] sctp: don't compare hb_timer expire date before starting it

[David Miller <davem@davemloft.net>]

From: kwiecienmaciek@gmail.com
Date: Fri, 22 Feb 2019 09:45:26 +0100

> From: Maciej Kwiecien <maciej.kwiecien@nokia.com>
> 
> 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@nokia.com>
> Tested-by: Marcin Stojek <marcin.stojek@nokia.com>
> Signed-off-by: Maciej Kwiecien <maciej.kwiecien@nokia.com>

Applied and queued up for -stable, thank you.