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@xxxxxxxxxxxxx>
---
drivers/infiniband/core/roce_gid_mgmt.c | 2 ++
include/linux/rtnetlink.h | 1 +
include/net/net_namespace.h | 1 +
net/core/dev.c | 5 +++++
net/core/fib_notifier.c | 2 ++
net/core/net_namespace.c | 18 +++++++++++++-----
net/core/rtnetlink.c | 5 +++++
net/netfilter/nf_conntrack_core.c | 2 ++
net/openvswitch/datapath.c | 2 ++
net/wireless/wext-core.c | 2 ++
security/selinux/include/xfrm.h | 2 ++
11 files changed, 37 insertions(+), 5 deletions(-)
diff --git a/drivers/infiniband/core/roce_gid_mgmt.c b/drivers/infiniband/core/roce_gid_mgmt.c
index 5a52ec77940a..cc2966380c0c 100644
--- a/drivers/infiniband/core/roce_gid_mgmt.c
+++ b/drivers/infiniband/core/roce_gid_mgmt.c
@@ -403,10 +403,12 @@ static void enum_all_gids_of_dev_cb(struct ib_device *ib_dev,
* our feet
*/
rtnl_lock();
+ down_read(&net_rwsem);
for_each_net(net)
for_each_netdev(net, ndev)
if (is_eth_port_of_netdev(ib_dev, port, rdma_ndev, ndev))
add_netdev_ips(ib_dev, port, rdma_ndev, ndev);
+ up_read(&net_rwsem);
rtnl_unlock();
}
diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index c7d1e4689325..5225832bd6ff 100644
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h
@@ -37,6 +37,7 @@ extern int rtnl_lock_killable(void);
extern wait_queue_head_t netdev_unregistering_wq;
extern struct rw_semaphore pernet_ops_rwsem;
+extern struct rw_semaphore net_rwsem;
#ifdef CONFIG_PROVE_LOCKING
extern bool lockdep_rtnl_is_held(void);
diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 1ab4f920f109..47e35cce3b64 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -291,6 +291,7 @@ static inline struct net *read_pnet(const possible_net_t *pnet)
#endif
}
+/* Protected by net_rwsem */
#define for_each_net(VAR) \
list_for_each_entry(VAR, &net_namespace_list, list)
diff --git a/net/core/dev.c b/net/core/dev.c
index e13807b5c84d..eca5458b2753 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1629,6 +1629,7 @@ int register_netdevice_notifier(struct notifier_block *nb)
goto unlock;
if (dev_boot_phase)
goto unlock;
+ down_read(&net_rwsem);
for_each_net(net) {
for_each_netdev(net, dev) {
err = call_netdevice_notifier(nb, NETDEV_REGISTER, dev);
@@ -1642,6 +1643,7 @@ int register_netdevice_notifier(struct notifier_block *nb)
call_netdevice_notifier(nb, NETDEV_UP, dev);
}
}
+ up_read(&net_rwsem);
unlock:
rtnl_unlock();
@@ -1664,6 +1666,7 @@ int register_netdevice_notifier(struct notifier_block *nb)
}
outroll:
+ up_read(&net_rwsem);
raw_notifier_chain_unregister(&netdev_chain, nb);
goto unlock;
}
@@ -1694,6 +1697,7 @@ int unregister_netdevice_notifier(struct notifier_block *nb)
if (err)
goto unlock;
+ down_read(&net_rwsem);
for_each_net(net) {
for_each_netdev(net, dev) {
if (dev->flags & IFF_UP) {
@@ -1704,6 +1708,7 @@ int unregister_netdevice_notifier(struct notifier_block *nb)
call_netdevice_notifier(nb, NETDEV_UNREGISTER, dev);
}
}
+ up_read(&net_rwsem);
unlock:
rtnl_unlock();
return err;
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;
diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index b5796d17a302..7fdf321d4997 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -33,6 +33,10 @@ static struct list_head *first_device = &pernet_list;
LIST_HEAD(net_namespace_list);
EXPORT_SYMBOL_GPL(net_namespace_list);
+/* Protects net_namespace_list. Nests iside rtnl_lock() */
+DECLARE_RWSEM(net_rwsem);
+EXPORT_SYMBOL_GPL(net_rwsem);
+
struct net init_net = {
.count = REFCOUNT_INIT(1),
.dev_base_head = LIST_HEAD_INIT(init_net.dev_base_head),
@@ -309,9 +313,9 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
if (error < 0)
goto out_undo;
}
- rtnl_lock();
+ down_write(&net_rwsem);
list_add_tail_rcu(&net->list, &net_namespace_list);
- rtnl_unlock();
+ up_write(&net_rwsem);
out:
return error;
@@ -450,7 +454,7 @@ static void unhash_nsid(struct net *net, struct net *last)
* and this work is the only process, that may delete
* a net from net_namespace_list. So, when the below
* is executing, the list may only grow. Thus, we do not
- * use for_each_net_rcu() or rtnl_lock().
+ * use for_each_net_rcu() or net_rwsem.
*/
for_each_net(tmp) {
int id;
@@ -485,7 +489,7 @@ static void cleanup_net(struct work_struct *work)
down_read(&pernet_ops_rwsem);
/* Don't let anyone else find us. */
- rtnl_lock();
+ down_write(&net_rwsem);
llist_for_each_entry(net, net_kill_list, cleanup_list)
list_del_rcu(&net->list);
/* Cache last net. After we unlock rtnl, no one new net
@@ -499,7 +503,7 @@ static void cleanup_net(struct work_struct *work)
* useless anyway, as netns_ids are destroyed there.
*/
last = list_last_entry(&net_namespace_list, struct net, list);
- rtnl_unlock();
+ up_write(&net_rwsem);
llist_for_each_entry(net, net_kill_list, cleanup_list) {
unhash_nsid(net, last);
@@ -900,6 +904,9 @@ static int __register_pernet_operations(struct list_head *list,
list_add_tail(&ops->list, list);
if (ops->init || (ops->id && ops->size)) {
+ /* We held write locked pernet_ops_rwsem, and parallel
+ * setup_net() and cleanup_net() are not possible.
+ */
for_each_net(net) {
error = ops_init(ops, net);
if (error)
@@ -923,6 +930,7 @@ static void __unregister_pernet_operations(struct pernet_operations *ops)
LIST_HEAD(net_exit_list);
list_del(&ops->list);
+ /* See comment in __register_pernet_operations() */
for_each_net(net)
list_add_tail(&net->exit_list, &net_exit_list);
ops_exit_list(ops, &net_exit_list);
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 2d3949789cef..e86b28482ca7 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -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;
diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 705198de671d..370f9b7f051b 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -1764,12 +1764,14 @@ nf_ct_iterate_destroy(int (*iter)(struct nf_conn *i, void *data), void *data)
struct net *net;
rtnl_lock();
+ down_read(&net_rwsem);
for_each_net(net) {
if (atomic_read(&net->ct.count) == 0)
continue;
__nf_ct_unconfirmed_destroy(net);
nf_queue_nf_hook_drop(net);
}
+ up_read(&net_rwsem);
rtnl_unlock();
/* Need to wait for netns cleanup worker to finish, if its
diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
index ef38e5aecd28..9746ee30a99b 100644
--- a/net/openvswitch/datapath.c
+++ b/net/openvswitch/datapath.c
@@ -2364,8 +2364,10 @@ static void __net_exit ovs_exit_net(struct net *dnet)
__dp_destroy(dp);
rtnl_lock();
+ down_read(&net_rwsem);
for_each_net(net)
list_vports_from_net(net, dnet, &head);
+ up_read(&net_rwsem);
rtnl_unlock();
/* Detach all vports from given namespace. */
diff --git a/net/wireless/wext-core.c b/net/wireless/wext-core.c
index 9efbfc753347..544d7b62d7ca 100644
--- a/net/wireless/wext-core.c
+++ b/net/wireless/wext-core.c
@@ -349,11 +349,13 @@ void wireless_nlevent_flush(void)
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);
diff --git a/security/selinux/include/xfrm.h b/security/selinux/include/xfrm.h
index 1f173a7a4daa..31d66431be1e 100644
--- a/security/selinux/include/xfrm.h
+++ b/security/selinux/include/xfrm.h
@@ -48,8 +48,10 @@ static inline void selinux_xfrm_notify_policyload(void)
struct net *net;
rtnl_lock();
+ down_read(&net_rwsem);
for_each_net(net)
rt_genid_bump_all(net);
+ up_read(&net_rwsem);
rtnl_unlock();
}
#else
--
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