net: dont hold rtnl mutex during netlink dump callbacks
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 :
1c2d670f366 : [RTNETLINK]: Hold rtnl_mutex during netlink dump callbacks
6313c1e0992 : [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>
diff --git a/net/decnet/dn_dev.c b/net/decnet/dn_dev.c
index 0dcaa90..404fa15 100644
--- a/net/decnet/dn_dev.c
+++ b/net/decnet/dn_dev.c
@@ -752,7 +752,8 @@
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) {
@@ -761,11 +762,11 @@
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;
@@ -778,6 +779,7 @@
idx++;
}
done:
+ rcu_read_unlock();
cb->args[0] = idx;
cb->args[1] = dn_idx;