diff mbox

sctp: Error in calculation of RTTvar

Message ID 1354115909-24172-1-git-send-email-vyasevich@gmail.com
State Accepted, archived
Delegated to: David Miller
Headers show

Commit Message

Vladislav Yasevich Nov. 28, 2012, 3:18 p.m. UTC 
From: Schoch Christian <e0326715@student.tuwien.ac.at>

The calculation of RTTVAR involves the subtraction of two unsigned
numbers which
may causes rollover and results in very high values of RTTVAR when RTT > SRTT.
With this patch it is possible to set RTOmin = 1 to get the minimum of RTO at
4 times the clock granularity.

Change Notes:

v2)
        *Replaced abs() by abs64() and long by __s64, changed patch
description.

Signed-off-by: Christian Schoch <e0326715@student.tuwien.ac.at>
CC: Vlad Yasevich <vyasevich@gmail.com>
CC: Sridhar Samudrala <sri@us.ibm.com>
CC: Neil Horman <nhorman@tuxdriver.com>
CC: linux-sctp@vger.kernel.org
Acked-by: Vlad Yasevich <vyasevich@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
---
 net/sctp/transport.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

Comments

David Miller Nov. 28, 2012, 4:13 p.m. UTC | #1 
From: vyasevich@gmail.com
Date: Wed, 28 Nov 2012 10:18:29 -0500

> From: Schoch Christian <e0326715@student.tuwien.ac.at>
> 
> The calculation of RTTVAR involves the subtraction of two unsigned
> numbers which
> may causes rollover and results in very high values of RTTVAR when RTT > SRTT.
> With this patch it is possible to set RTOmin = 1 to get the minimum of RTO at
> 4 times the clock granularity.
> 
> Change Notes:
> 
> v2)
>         *Replaced abs() by abs64() and long by __s64, changed patch
> description.
> 
> Signed-off-by: Christian Schoch <e0326715@student.tuwien.ac.at>
> CC: Vlad Yasevich <vyasevich@gmail.com>
> CC: Sridhar Samudrala <sri@us.ibm.com>
> CC: Neil Horman <nhorman@tuxdriver.com>
> CC: linux-sctp@vger.kernel.org
> Acked-by: Vlad Yasevich <vyasevich@gmail.com>
> Acked-by: Neil Horman <nhorman@tuxdriver.com>

Applied, thanks.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
diff mbox

Patch

diff --git a/net/sctp/transport.c b/net/sctp/transport.c
index 953c21e..206cf52 100644
--- a/net/sctp/transport.c
+++ b/net/sctp/transport.c
@@ -331,7 +331,7 @@  void sctp_transport_update_rto(struct sctp_transport *tp, __u32 rtt)
 		 * 1/8, rto_alpha would be expressed as 3.
 		 */
 		tp->rttvar = tp->rttvar - (tp->rttvar >> net->sctp.rto_beta)
-			+ ((abs(tp->srtt - rtt)) >> net->sctp.rto_beta);
+			+ (((__u32)abs64((__s64)tp->srtt - (__s64)rtt)) >> net->sctp.rto_beta);
 		tp->srtt = tp->srtt - (tp->srtt >> net->sctp.rto_alpha)
 			+ (rtt >> net->sctp.rto_alpha);
 	} else {