ipv4: avoid quadratic behavior in netns dismantle

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: bb138aa120b5 ("net: Make ifindex generation per-net namespace")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 45619c005b8dddd7ccd5c7029efa4ed69b6ce1de..9813949da10493de36b9db797b6a5d94fd9bd3b1 100644 (file)
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -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>
@@ -319,11 +320,15 @@ 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,
@@ -433,12 +438,11 @@ 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 &&
@@ -1609,12 +1613,10 @@ link_it:
        } 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)
        }
@@ -1966,8 +1968,7 @@ 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) {
@@ -1986,12 +1987,11 @@ 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;
@@ -2136,7 +2136,6 @@ out:
 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;
@@ -2152,8 +2151,7 @@ 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) {