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net: do not create fallback tunnels for non-default namespaces

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fallback tunnels (like tunl0, gre0, gretap0, erspan0, sit0,
ip6tnl0, ip6gre0) are automatically created when the corresponding
module is loaded.

These tunnels are also automatically created when a new network
namespace is created, at a great cost.

In many cases, netns are used for isolation purposes, and these
extra network devices are a waste of resources. We are using
thousands of netns per host, and hit the netns creation/delete
bottleneck a lot. (Many thanks to Kirill for recent work on this)

Add a new sysctl so that we can opt-out from this automatic creation.

Note that these tunnels are still created for the initial namespace,
to be the least intrusive for typical setups.

Tested:
lpk43:~# cat add_del_unshare.sh
for i in `seq 1 40`
do
 (for j in `seq 1 100` ; do  unshare -n /bin/true >/dev/null ; done) &
done
wait

lpk43:~# echo 0 >/proc/sys/net/core/fb_tunnels_only_for_init_net
lpk43:~# time ./add_del_unshare.sh

real	0m37.521s
user	0m0.886s
sys	7m7.084s
lpk43:~# echo 1 >/proc/sys/net/core/fb_tunnels_only_for_init_net
lpk43:~# time ./add_del_unshare.sh

real	0m4.761s
user	0m0.851s
sys	1m8.343s
lpk43:~#

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet
2018-03-08 12:51:41 -08:00
committed by David S. Miller
parent 2b3905de8b
commit 79134e6ce2
8 changed files with 54 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
net/ipv6/ip6_gre.c
View File

@@ -236,7 +236,7 @@ static struct ip6_tnl *ip6gre_tunnel_lookup(struct net_device *dev,
return t;
dev = ign->fb_tunnel_dev;
if (dev->flags & IFF_UP)
if (dev && dev->flags & IFF_UP)
return netdev_priv(dev);
return NULL;
@@ -1472,6 +1472,8 @@ static int __net_init ip6gre_init_net(struct net *net)
struct ip6gre_net *ign = net_generic(net, ip6gre_net_id);
int err;
if (!net_has_fallback_tunnels(net))
return 0;
ign->fb_tunnel_dev = alloc_netdev(sizeof(struct ip6_tnl), "ip6gre0",
NET_NAME_UNKNOWN,
ip6gre_tunnel_setup);

2
net/ipv6/ip6_tunnel.c
View File

@@ -2205,6 +2205,8 @@ static int __net_init ip6_tnl_init_net(struct net *net)
ip6n->tnls[0] = ip6n->tnls_wc;
ip6n->tnls[1] = ip6n->tnls_r_l;
if (!net_has_fallback_tunnels(net))
return 0;
err = -ENOMEM;
ip6n->fb_tnl_dev = alloc_netdev(sizeof(struct ip6_tnl), "ip6tnl0",
NET_NAME_UNKNOWN, ip6_tnl_dev_setup);

5
net/ipv6/sit.c
View File

@@ -182,7 +182,7 @@ static void ipip6_tunnel_clone_6rd(struct net_device *dev, struct sit_net *sitn)
#ifdef CONFIG_IPV6_SIT_6RD
struct ip_tunnel *t = netdev_priv(dev);
if (dev == sitn->fb_tunnel_dev) {
if (dev == sitn->fb_tunnel_dev || !sitn->fb_tunnel_dev) {
ipv6_addr_set(&t->ip6rd.prefix, htonl(0x20020000), 0, 0, 0);
t->ip6rd.relay_prefix = 0;
t->ip6rd.prefixlen = 16;
@@ -1835,6 +1835,9 @@ static int __net_init sit_init_net(struct net *net)
sitn->tunnels[2] = sitn->tunnels_r;
sitn->tunnels[3] = sitn->tunnels_r_l;
if (!net_has_fallback_tunnels(net))
return 0;
sitn->fb_tunnel_dev = alloc_netdev(sizeof(struct ip_tunnel), "sit0",
NET_NAME_UNKNOWN,
ipip6_tunnel_setup);