netdev - Re: PATCH: ipv6: avoid wraparound for expired lifetimes

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Message-ID: <20090625090603.GP21357@jayr.de>
Date:	Thu, 25 Jun 2009 11:06:03 +0200
From:	Jens Rosenboom <me@...r.de>
To:	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
Cc:	Jens Rosenboom <me@...r.de>, Netdev <netdev@...r.kernel.org>
Subject: Re: PATCH: ipv6: avoid wraparound for expired lifetimes

On Thu, Jun 25, 2009 at 11:40:19AM +0300, Ilpo Järvinen wrote:
> On Thu, 25 Jun 2009, Jens Rosenboom wrote:
> 
> > If the valid or preferred lifetime for an address expires, the kernel
> > shows huge values for these due to a counter wrap,
> 
> I suspect we have plenty of potentially counter-wrapped printouts all 
> around the kernel. So you're fixing just a tip of the iceberg.

So are you implying that because I don't fix all of them at once, I
shouldn't bother to start at all?

On Thu, 2009-06-25 at 01:42 -0700, David Miller wrote:
...
> Jens, don't even bother posting patches that fail to
> build.

Sorry for that, here is the correct version.

--- linux-2.6.30.orig/net/ipv6/addrconf.c	2009-06-10 05:05:27.000000000 +0200
+++ linux-2.6.30/net/ipv6/addrconf.c	2009-06-25 10:52:27.000000000 +0200
@@ -3361,9 +3361,18 @@
 		valid = ifa->valid_lft;
 		if (preferred != INFINITY_LIFE_TIME) {
 			long tval = (jiffies - ifa->tstamp)/HZ;
-			preferred -= tval;
-			if (valid != INFINITY_LIFE_TIME)
-				valid -= tval;
+			if (preferred > tval) {
+				preferred -= tval;
+			} else {
+				preferred = 0;
+			}
+			if (valid != INFINITY_LIFE_TIME) {
+				if (valid > tval) {
+					valid -= tval;
+				} else {
+					valid = 0;
+				}
+			}
 		}
 	} else {
 		preferred = INFINITY_LIFE_TIME;

And to show you where this appears:

Output with plain 2.6.30

# ip -6 addr show dev eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qlen 1000
    inet6 2001:db8::202:a5ff:fee8:20be/64 scope global dynamic 
       valid_lft 870sec preferred_lft 7sec
    inet6 fe80::202:a5ff:fee8:20be/64 scope link 
       valid_lft forever preferred_lft forever
# sleep 30
# ip -6 addr show dev eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qlen 1000
    inet6 2001:db8::202:a5ff:fee8:20be/64 scope global deprecated dynamic 
       valid_lft 840sec preferred_lft 4294967266sec
    inet6 fe80::202:a5ff:fee8:20be/64 scope link 
       valid_lft forever preferred_lft forever

Output with patched 2.6.30

# ip -6 addr show dev eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qlen 1000
    inet6 2001:db8::202:a5ff:fee8:12e1/64 scope global dynamic 
       valid_lft 897sec preferred_lft 27sec
    inet6 fe80::202:a5ff:fee8:12e1/64 scope link 
       valid_lft forever preferred_lft forever
# sleep 30
# ip -6 addr show dev eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qlen 1000
    inet6 2001:db8::202:a5ff:fee8:12e1/64 scope global deprecated dynamic 
       valid_lft 862sec preferred_lft 0sec
    inet6 fe80::202:a5ff:fee8:12e1/64 scope link 
       valid_lft forever preferred_lft forever

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