net: Introduce net_rwsem to protect net_namespace_list
rtnl_lock() is used everywhere, and contention is very high.
When someone wants to iterate over alive net namespaces,
he/she has no a possibility to do that without exclusive lock.
But the exclusive rtnl_lock() in such places is overkill,
and it just increases the contention. Yes, there is already
for_each_net_rcu() in kernel, but it requires rcu_read_lock(),
and this can't be sleepable. Also, sometimes it may be need
really prevent net_namespace_list growth, so for_each_net_rcu()
is not fit there.
This patch introduces new rw_semaphore, which will be used
instead of rtnl_mutex to protect net_namespace_list. It is
sleepable and allows not-exclusive iterations over net
namespaces list. It allows to stop using rtnl_lock()
in several places (what is made in next patches) and makes
less the time, we keep rtnl_mutex. Here we just add new lock,
while the explanation of we can remove rtnl_lock() there are
in next patches.
Fine grained locks generally are better, then one big lock,
so let's do that with net_namespace_list, while the situation
allows that.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/wireless/wext-core.c b/net/wireless/wext-core.c
index 9efbfc7..544d7b6 100644
--- a/net/wireless/wext-core.c
+++ b/net/wireless/wext-core.c
@@ -349,11 +349,13 @@
ASSERT_RTNL();
+ down_read(&net_rwsem);
for_each_net(net) {
while ((skb = skb_dequeue(&net->wext_nlevents)))
rtnl_notify(skb, net, 0, RTNLGRP_LINK, NULL,
GFP_KERNEL);
}
+ up_read(&net_rwsem);
}
EXPORT_SYMBOL_GPL(wireless_nlevent_flush);