netdev - Re: [PATCH net 1/2] ipv6: reset dst.expires value when clearing expire flag

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Message-ID: <1382596613.7572.42.camel@edumazet-glaptop.roam.corp.google.com>
Date:	Wed, 23 Oct 2013 23:36:53 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	netdev@...r.kernel.org, sgunderson@...foot.com, valentyn@...b.net,
	yoshfuji@...ux-ipv6.org
Subject: Re: [PATCH net 1/2] ipv6: reset dst.expires value when clearing
 expire flag

On Thu, 2013-10-24 at 07:48 +0200, Hannes Frederic Sowa wrote:
> On receiving a packet too big icmp error we update the expire value by
> calling rt6_update_expires. This function uses dst_set_expires which is
> implemented that it can only reduce the expiration value of the dst entry.
> 
> If we insert new routing non-expiry information into the ipv6 fib where
> we already have a matching rt6_info we only clear the RTF_EXPIRES flag
> in rt6i_flags and leave the dst.expires value as is.
> 
> When new mtu information arrives for that cached dst_entry we again
> call dst_set_expires. This time it won't update the dst.expire value
> because we left the dst.expire value intact from the last update. So
> dst_set_expires won't touch dst.expires.
> 
> Fix this by resetting dst.expires when clearing the RTF_EXPIRE flag.
> dst_set_expires checks for a zero expiration and updates the
> dst.expires.
> 
> In the past this (not updating dst.expires) was necessary because
> dst.expire was placed in a union with the dst_entry *from reference. So
> an update on the value would have caused page faults. This split happend
> in ecd9883724b78cc72ed92c98bcb1a46c764fff21 ("ipv6: fix race condition
> regarding dst->expires and dst->from").
> 

Well, this patch removed the :

rt->dst.from = NULL;

from rt6_clean_expires(), right ?

Acked-by: Eric Dumazet <edumazet@...gle.com>



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