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Commit 682a1e0e authored by Eric Dumazet's avatar Eric Dumazet Committed by Greg Kroah-Hartman
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ipv4: avoid quadratic behavior in netns dismantle 



commit d07418afea8f1d9896aaf9dc5ae47ac4f45b220c upstream.

net/ipv4/fib_semantics.c uses an hash table of 256 slots,
keyed by device ifindexes: fib_info_devhash[DEVINDEX_HASHSIZE]

Problem is that with network namespaces, devices tend
to use the same ifindex.

lo device for instance has a fixed ifindex of one,
for all network namespaces.

This means that hosts with thousands of netns spend
a lot of time looking at some hash buckets with thousands
of elements, notably at netns dismantle.

Simply add a per netns perturbation (net_hash_mix())
to spread elements more uniformely.

Also change fib_devindex_hashfn() to use more entropy.

Fixes: aa79e66e ("net: Make ifindex generation per-net namespace")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reviewed-by: default avatarDavid Ahern <dsahern@kernel.org>
Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent e6669fba

net/ipv4/fib_semantics.c

+17 −19
Original line number Diff line number Diff line
@@ -29,6 +29,7 @@ 
#include <linux/init.h>

#include <linux/slab.h>

#include <linux/netlink.h>

#include <linux/hash.h>



#include <net/arp.h>

#include <net/ip.h>
@@ -318,11 +319,15 @@ static inline int nh_comp(struct fib_info *fi, struct fib_info *ofi) 


static inline unsigned int fib_devindex_hashfn(unsigned int val)

{

	unsigned int mask = DEVINDEX_HASHSIZE - 1;

	return hash_32(val, DEVINDEX_HASHBITS);

}



static struct hlist_head *

fib_info_devhash_bucket(const struct net_device *dev)

{

	u32 val = net_hash_mix(dev_net(dev)) ^ dev->ifindex;



	return (val ^

		(val >> DEVINDEX_HASHBITS) ^

		(val >> (DEVINDEX_HASHBITS * 2))) & mask;

	return &fib_info_devhash[fib_devindex_hashfn(val)];

}



static unsigned int fib_info_hashfn_1(int init_val, u8 protocol, u8 scope,
@@ -432,12 +437,11 @@ int ip_fib_check_default(__be32 gw, struct net_device *dev) 
{

	struct hlist_head *head;

	struct fib_nh *nh;

	unsigned int hash;



	spin_lock(&fib_info_lock);



	hash = fib_devindex_hashfn(dev->ifindex);

	head = &fib_info_devhash[hash];

	head = fib_info_devhash_bucket(dev);



	hlist_for_each_entry(nh, head, nh_hash) {

		if (nh->fib_nh_dev == dev &&

		    nh->fib_nh_gw4 == gw &&
@@ -1594,12 +1598,10 @@ struct fib_info *fib_create_info(struct fib_config *cfg, 
	} else {

		change_nexthops(fi) {

			struct hlist_head *head;

			unsigned int hash;



			if (!nexthop_nh->fib_nh_dev)

				continue;

			hash = fib_devindex_hashfn(nexthop_nh->fib_nh_dev->ifindex);

			head = &fib_info_devhash[hash];

			head = fib_info_devhash_bucket(nexthop_nh->fib_nh_dev);

			hlist_add_head(&nexthop_nh->nh_hash, head);

		} endfor_nexthops(fi)

	}
@@ -1940,8 +1942,7 @@ void fib_nhc_update_mtu(struct fib_nh_common *nhc, u32 new, u32 orig) 


void fib_sync_mtu(struct net_device *dev, u32 orig_mtu)

{

	unsigned int hash = fib_devindex_hashfn(dev->ifindex);

	struct hlist_head *head = &fib_info_devhash[hash];

	struct hlist_head *head = fib_info_devhash_bucket(dev);

	struct fib_nh *nh;



	hlist_for_each_entry(nh, head, nh_hash) {
@@ -1960,12 +1961,11 @@ void fib_sync_mtu(struct net_device *dev, u32 orig_mtu) 
 */

int fib_sync_down_dev(struct net_device *dev, unsigned long event, bool force)

{

	int ret = 0;

	int scope = RT_SCOPE_NOWHERE;

	struct hlist_head *head = fib_info_devhash_bucket(dev);

	struct fib_info *prev_fi = NULL;

	unsigned int hash = fib_devindex_hashfn(dev->ifindex);

	struct hlist_head *head = &fib_info_devhash[hash];

	int scope = RT_SCOPE_NOWHERE;

	struct fib_nh *nh;

	int ret = 0;



	if (force)

		scope = -1;
@@ -2110,7 +2110,6 @@ static void fib_select_default(const struct flowi4 *flp, struct fib_result *res) 
int fib_sync_up(struct net_device *dev, unsigned char nh_flags)

{

	struct fib_info *prev_fi;

	unsigned int hash;

	struct hlist_head *head;

	struct fib_nh *nh;

	int ret;
@@ -2126,8 +2125,7 @@ int fib_sync_up(struct net_device *dev, unsigned char nh_flags) 
	}



	prev_fi = NULL;

	hash = fib_devindex_hashfn(dev->ifindex);

	head = &fib_info_devhash[hash];

	head = fib_info_devhash_bucket(dev);

	ret = 0;



	hlist_for_each_entry(nh, head, nh_hash) {