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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 :

1c2d670f36 : [RTNETLINK]: Hold rtnl_mutex during netlink dump callbacks
6313c1e099 : [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>
This commit is contained in:
Eric Dumazet 2011-04-27 22:56:07 +00:00 • committed by David S. Miller
parent dcfd9cdc12
commit e67f88dd12
8 changed files with 25 additions and 23 deletions
Download patch file Download diff file Expand all files Collapse all files

12
net/core/rtnetlink.c
View file

@ -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,
@ -1023,6 +1024,7 @@ cont:
}
}
out:
rcu_read_unlock();
cb->args[1] = idx;
cb->args[0] = h;
@ -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)
@ -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 *)));
@ -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;