From f0b07bb151b098d291fd1fd71ef7a2df56fb124a Mon Sep 17 00:00:00 2001 From: Kirill Tkhai Date: Thu, 29 Mar 2018 19:20:32 +0300 Subject: 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 Signed-off-by: David S. Miller --- net/core/fib_notifier.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'net/core/fib_notifier.c') diff --git a/net/core/fib_notifier.c b/net/core/fib_notifier.c index 0c048bdeb016..614b985c92a4 100644 --- a/net/core/fib_notifier.c +++ b/net/core/fib_notifier.c @@ -33,6 +33,7 @@ static unsigned int fib_seq_sum(void) struct net *net; rtnl_lock(); + down_read(&net_rwsem); for_each_net(net) { rcu_read_lock(); list_for_each_entry_rcu(ops, &net->fib_notifier_ops, list) { @@ -43,6 +44,7 @@ static unsigned int fib_seq_sum(void) } rcu_read_unlock(); } + up_read(&net_rwsem); rtnl_unlock(); return fib_seq; -- cgit