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net: dont hold rtnl mutex during netlink dump callbacks
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Four years ago, Patrick made a change to hold rtnl mutex during netlink
dump callbacks.

I believe it was a wrong move. This slows down concurrent dumps, making
good old /proc/net/ files faster than rtnetlink in some situations.

This occurred to me because one "ip link show dev ..." was _very_ slow
on a workload adding/removing network devices in background.

All dump callbacks are able to use RCU locking now, so this patch does
roughly a revert of commits :

1c2d670 : [RTNETLINK]: Hold rtnl_mutex during netlink dump callbacks
6313c1e : [RTNETLINK]: Remove unnecessary locking in dump callbacks

This let writers fight for rtnl mutex and readers going full speed.

It also takes care of phonet : phonet_route_get() is now called from rcu
read section. I renamed it to phonet_route_get_rcu()

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Patrick McHardy <kaber@trash.net>
Cc: Remi Denis-Courmont <remi.denis-courmont@nokia.com>
Acked-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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@davem330
Eric Dumazet authored and davem330 committed May 2, 2011
1 parent dcfd9cd commit e67f88d
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Showing 8 changed files with 25 additions and 23 deletions.
2 changes: 1 addition & 1 deletion include/net/phonet/pn_dev.h
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Original file line number Diff line number Diff line change
Expand Up @@ -51,7 +51,7 @@ void phonet_address_notify(int event, struct net_device *dev, u8 addr);
int phonet_route_add(struct net_device *dev, u8 daddr);
int phonet_route_del(struct net_device *dev, u8 daddr);
void rtm_phonet_notify(int event, struct net_device *dev, u8 dst);
struct net_device *phonet_route_get(struct net *net, u8 daddr);
struct net_device *phonet_route_get_rcu(struct net *net, u8 daddr);
struct net_device *phonet_route_output(struct net *net, u8 daddr);

#define PN_NO_ADDR 0xff
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7 changes: 4 additions & 3 deletions net/bridge/br_netlink.c
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Original file line number Diff line number Diff line change
Expand Up @@ -120,8 +120,9 @@ static int br_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
int idx;

idx = 0;
for_each_netdev(net, dev) {
struct net_bridge_port *port = br_port_get_rtnl(dev);
rcu_read_lock();
for_each_netdev_rcu(net, dev) {
struct net_bridge_port *port = br_port_get_rcu(dev);

/* not a bridge port */
if (!port || idx < cb->args[0])
Expand All @@ -135,7 +136,7 @@ static int br_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
skip:
++idx;
}

rcu_read_unlock();
cb->args[0] = idx;

return skb->len;
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3 changes: 2 additions & 1 deletion net/core/fib_rules.c
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Original file line number Diff line number Diff line change
Expand Up @@ -590,7 +590,8 @@ static int dump_rules(struct sk_buff *skb, struct netlink_callback *cb,
int idx = 0;
struct fib_rule *rule;

list_for_each_entry(rule, &ops->rules_list, list) {
rcu_read_lock();
list_for_each_entry_rcu(rule, &ops->rules_list, list) {
if (idx < cb->args[1])
goto skip;

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12 changes: 5 additions & 7 deletions net/core/rtnetlink.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1007,10 +1007,11 @@ static int rtnl_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
s_h = cb->args[0];
s_idx = cb->args[1];

rcu_read_lock();
for (h = s_h; h < NETDEV_HASHENTRIES; h++, s_idx = 0) {
idx = 0;
head = &net->dev_index_head[h];
hlist_for_each_entry(dev, node, head, index_hlist) {
hlist_for_each_entry_rcu(dev, node, head, index_hlist) {
if (idx < s_idx)
goto cont;
if (rtnl_fill_ifinfo(skb, dev, RTM_NEWLINK,
Expand All @@ -1023,6 +1024,7 @@ static int rtnl_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
}
}
out:
rcu_read_unlock();
cb->args[1] = idx;
cb->args[0] = h;

Expand Down Expand Up @@ -1879,7 +1881,6 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
int min_len;
int family;
int type;
int err;

type = nlh->nlmsg_type;
if (type > RTM_MAX)
Expand All @@ -1906,11 +1907,8 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
if (dumpit == NULL)
return -EOPNOTSUPP;

__rtnl_unlock();
rtnl = net->rtnl;
err = netlink_dump_start(rtnl, skb, nlh, dumpit, NULL);
rtnl_lock();
return err;
return netlink_dump_start(rtnl, skb, nlh, dumpit, NULL);
}

memset(rta_buf, 0, (rtattr_max * sizeof(struct rtattr *)));
Expand Down Expand Up @@ -1980,7 +1978,7 @@ static int __net_init rtnetlink_net_init(struct net *net)
{
struct sock *sk;
sk = netlink_kernel_create(net, NETLINK_ROUTE, RTNLGRP_MAX,
rtnetlink_rcv, &rtnl_mutex, THIS_MODULE);
rtnetlink_rcv, NULL, THIS_MODULE);
if (!sk)
return -ENOMEM;
net->rtnl = sk;
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10 changes: 6 additions & 4 deletions net/decnet/dn_dev.c
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Original file line number Diff line number Diff line change
Expand Up @@ -752,7 +752,8 @@ static int dn_nl_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
skip_naddr = cb->args[1];

idx = 0;
for_each_netdev(&init_net, dev) {
rcu_read_lock();
for_each_netdev_rcu(&init_net, dev) {
if (idx < skip_ndevs)
goto cont;
else if (idx > skip_ndevs) {
Expand All @@ -761,11 +762,11 @@ static int dn_nl_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
skip_naddr = 0;
}

if ((dn_db = rtnl_dereference(dev->dn_ptr)) == NULL)
if ((dn_db = rcu_dereference(dev->dn_ptr)) == NULL)
goto cont;

for (ifa = rtnl_dereference(dn_db->ifa_list), dn_idx = 0; ifa;
ifa = rtnl_dereference(ifa->ifa_next), dn_idx++) {
for (ifa = rcu_dereference(dn_db->ifa_list), dn_idx = 0; ifa;
ifa = rcu_dereference(ifa->ifa_next), dn_idx++) {
if (dn_idx < skip_naddr)
continue;

Expand All @@ -778,6 +779,7 @@ static int dn_nl_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
idx++;
}
done:
rcu_read_unlock();
cb->args[0] = idx;
cb->args[1] = dn_idx;

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4 changes: 3 additions & 1 deletion net/ipv6/ip6_fib.c
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Original file line number Diff line number Diff line change
Expand Up @@ -394,10 +394,11 @@ static int inet6_dump_fib(struct sk_buff *skb, struct netlink_callback *cb)
arg.net = net;
w->args = &arg;

rcu_read_lock();
for (h = s_h; h < FIB6_TABLE_HASHSZ; h++, s_e = 0) {
e = 0;
head = &net->ipv6.fib_table_hash[h];
hlist_for_each_entry(tb, node, head, tb6_hlist) {
hlist_for_each_entry_rcu(tb, node, head, tb6_hlist) {
if (e < s_e)
goto next;
res = fib6_dump_table(tb, skb, cb);
Expand All @@ -408,6 +409,7 @@ static int inet6_dump_fib(struct sk_buff *skb, struct netlink_callback *cb)
}
}
out:
rcu_read_unlock();
cb->args[1] = e;
cb->args[0] = h;

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6 changes: 1 addition & 5 deletions net/phonet/pn_dev.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -426,18 +426,14 @@ int phonet_route_del(struct net_device *dev, u8 daddr)
return 0;
}

struct net_device *phonet_route_get(struct net *net, u8 daddr)
struct net_device *phonet_route_get_rcu(struct net *net, u8 daddr)
{
struct phonet_net *pnn = phonet_pernet(net);
struct phonet_routes *routes = &pnn->routes;
struct net_device *dev;

ASSERT_RTNL(); /* no need to hold the device */

daddr >>= 2;
rcu_read_lock();
dev = rcu_dereference(routes->table[daddr]);
rcu_read_unlock();
return dev;
}

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4 changes: 3 additions & 1 deletion net/phonet/pn_netlink.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -264,10 +264,11 @@ static int route_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
struct net *net = sock_net(skb->sk);
u8 addr, addr_idx = 0, addr_start_idx = cb->args[0];

rcu_read_lock();
for (addr = 0; addr < 64; addr++) {
struct net_device *dev;

dev = phonet_route_get(net, addr << 2);
dev = phonet_route_get_rcu(net, addr << 2);
if (!dev)
continue;

Expand All @@ -279,6 +280,7 @@ static int route_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
}

out:
rcu_read_unlock();
cb->args[0] = addr_idx;
cb->args[1] = 0;

Expand Down

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