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net: Introduce net_rwsem to protect net_namespace_list

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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>
This commit is contained in:
Kirill Tkhai
2018-03-29 19:20:32 +03:00
committed by David S. Miller
parent 906edee91e
commit f0b07bb151
11 changed files with 37 additions and 5 deletions
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5
net/core/rtnetlink.c
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@@ -418,9 +418,11 @@ void __rtnl_link_unregister(struct rtnl_link_ops *ops)
{
struct net *net;
down_read(&net_rwsem);
for_each_net(net) {
__rtnl_kill_links(net, ops);
}
up_read(&net_rwsem);
list_del(&ops->list);
}
EXPORT_SYMBOL_GPL(__rtnl_link_unregister);
@@ -438,6 +440,9 @@ static void rtnl_lock_unregistering_all(void)
for (;;) {
unregistering = false;
rtnl_lock();
/* We held write locked pernet_ops_rwsem, and parallel
* setup_net() and cleanup_net() are not possible.
*/
for_each_net(net) {
if (net->dev_unreg_count > 0) {
unregistering = true;