netdev - Re: [PATCH] ipv4 routing: Fixes to allow route cache entries to work when route caching is disabled

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Message-Id: <20090623.163715.181992690.davem@davemloft.net>
Date:	Tue, 23 Jun 2009 16:37:15 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	nhorman@...driver.com
Cc:	jarkao2@...il.com, netdev@...r.kernel.org, kuznet@....inr.ac.ru,
	pekkas@...core.fi, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
	kaber@...sh.net, mbizon@...ebox.fr
Subject: Re: [PATCH] ipv4 routing: Fixes to allow route cache entries to
 work when route caching is disabled

From: Neil Horman <nhorman@...driver.com>
Date: Mon, 22 Jun 2009 16:18:53 -0400

> Ensure that route cache entries are usable and reclaimable with caching is off
> 
> When route caching is disabled (rt_caching returns false), We still use route
> cache entries that are created and passed into rt_intern_hash once.  These
> routes need to be made usable for the one call path that holds a reference to
> them, and they need to be reclaimed when they're finished with their use.  To be
> made usable, they need to be associated with a neighbor table entry (which they
> currently are not), otherwise iproute_finish2 just discards the packet, since we
> don't know which L2 peer to send the packet to.  To do this binding, we need to
> follow the path a bit higher up in rt_intern_hash, which calls
> arp_bind_neighbour, but not assign the route entry to the hash table.
> Currently, if caching is off, we simply assign the route to the rp pointer and
> are reutrn success.  This patch associates us with a neighbor entry first.
> 
> Secondly, we need to make sure that any single use routes like this are known to
> the garbage collector when caching is off.  If caching is off, and we try to
> hash in a route, it will leak when its refcount reaches zero.  To avoid this,
> this patch calls rt_free on the route cache entry passed into rt_intern_hash.
> This places us on the gc list for the route cache garbage collector, so that
> when its refcount reaches zero, it will be reclaimed (Thanks to Alexey for this
> suggestion).
> 
> I've tested this on a local system here, and with these patches in place, I'm
> able to maintain routed connectivity to remote systems, even if I set
> /proc/sys/net/ipv4/rt_cache_rebuild_count to -1, which forces rt_caching to
> return false.
> 
> Signed-off-by: Neil Horman <nhorman@...hat.com>
> Reported-by: Jarek Poplawski <jarkao2@...il.com>
> Reported-by: Maxime Bizon <mbizon@...ebox.fr>

Applied, thanks!
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