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authorKirill Tkhai <ktkhai@virtuozzo.com>2018-02-13 12:26:23 +0300
committerDavid S. Miller <davem@davemloft.net>2018-02-13 18:36:04 +0300
commit1a57feb847c56d6193f67d0e892c24e71f9e3ab1 (patch)
tree3e09866e7e939a6a350eb3385478260cfed4c101
parent5ba049a5cc8e24a1643df75bbf65b4efa070fa74 (diff)
downloadlinux-1a57feb847c56d6193f67d0e892c24e71f9e3ab1.tar.xz
net: Introduce net_sem for protection of pernet_list
Currently, the mutex is mostly used to protect pernet operations list. It orders setup_net() and cleanup_net() with parallel {un,}register_pernet_operations() calls, so ->exit{,batch} methods of the same pernet operations are executed for a dying net, as were used to call ->init methods, even after the net namespace is unlinked from net_namespace_list in cleanup_net(). But there are several problems with scalability. The first one is that more than one net can't be created or destroyed at the same moment on the node. For big machines with many cpus running many containers it's very sensitive. The second one is that it's need to synchronize_rcu() after net is removed from net_namespace_list(): Destroy net_ns: cleanup_net() mutex_lock(&net_mutex) list_del_rcu(&net->list) synchronize_rcu() <--- Sleep there for ages list_for_each_entry_reverse(ops, &pernet_list, list) ops_exit_list(ops, &net_exit_list) list_for_each_entry_reverse(ops, &pernet_list, list) ops_free_list(ops, &net_exit_list) mutex_unlock(&net_mutex) This primitive is not fast, especially on the systems with many processors and/or when preemptible RCU is enabled in config. So, all the time, while cleanup_net() is waiting for RCU grace period, creation of new net namespaces is not possible, the tasks, who makes it, are sleeping on the same mutex: Create net_ns: copy_net_ns() mutex_lock_killable(&net_mutex) <--- Sleep there for ages I observed 20-30 seconds hangs of "unshare -n" on ordinary 8-cpu laptop with preemptible RCU enabled after CRIU tests round is finished. The solution is to convert net_mutex to the rw_semaphore and add fine grain locks to really small number of pernet_operations, what really need them. Then, pernet_operations::init/::exit methods, modifying the net-related data, will require down_read() locking only, while down_write() will be used for changing pernet_list (i.e., when modules are being loaded and unloaded). This gives signify performance increase, after all patch set is applied, like you may see here: %for i in {1..10000}; do unshare -n bash -c exit; done *before* real 1m40,377s user 0m9,672s sys 0m19,928s *after* real 0m17,007s user 0m5,311s sys 0m11,779 (5.8 times faster) This patch starts replacing net_mutex to net_sem. It adds rw_semaphore, describes the variables it protects, and makes to use, where appropriate. net_mutex is still present, and next patches will kick it out step-by-step. Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com> Acked-by: Andrei Vagin <avagin@virtuozzo.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--include/linux/rtnetlink.h1
-rw-r--r--net/core/net_namespace.c39
-rw-r--r--net/core/rtnetlink.c4
3 files changed, 29 insertions, 15 deletions
diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index 1fdcde96eb65..e9ee9ad0a681 100644
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h
@@ -36,6 +36,7 @@ extern int rtnl_is_locked(void);
extern wait_queue_head_t netdev_unregistering_wq;
extern struct mutex net_mutex;
+extern struct rw_semaphore net_sem;
#ifdef CONFIG_PROVE_LOCKING
extern bool lockdep_rtnl_is_held(void);
diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 81384386f91b..e89b2b7abd36 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -41,6 +41,11 @@ struct net init_net = {
EXPORT_SYMBOL(init_net);
static bool init_net_initialized;
+/*
+ * net_sem: protects: pernet_list, net_generic_ids,
+ * init_net_initialized and first_device pointer.
+ */
+DECLARE_RWSEM(net_sem);
#define MIN_PERNET_OPS_ID \
((sizeof(struct net_generic) + sizeof(void *) - 1) / sizeof(void *))
@@ -286,7 +291,7 @@ struct net *get_net_ns_by_id(struct net *net, int id)
*/
static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
{
- /* Must be called with net_mutex held */
+ /* Must be called with net_sem held */
const struct pernet_operations *ops, *saved_ops;
int error = 0;
LIST_HEAD(net_exit_list);
@@ -418,12 +423,16 @@ struct net *copy_net_ns(unsigned long flags,
net->ucounts = ucounts;
get_user_ns(user_ns);
- rv = mutex_lock_killable(&net_mutex);
+ rv = down_read_killable(&net_sem);
if (rv < 0)
goto put_userns;
-
+ rv = mutex_lock_killable(&net_mutex);
+ if (rv < 0)
+ goto up_read;
rv = setup_net(net, user_ns);
mutex_unlock(&net_mutex);
+up_read:
+ up_read(&net_sem);
if (rv < 0) {
put_userns:
put_user_ns(user_ns);
@@ -477,6 +486,7 @@ static void cleanup_net(struct work_struct *work)
list_replace_init(&cleanup_list, &net_kill_list);
spin_unlock_irq(&cleanup_list_lock);
+ down_read(&net_sem);
mutex_lock(&net_mutex);
/* Don't let anyone else find us. */
@@ -517,6 +527,7 @@ static void cleanup_net(struct work_struct *work)
ops_free_list(ops, &net_exit_list);
mutex_unlock(&net_mutex);
+ up_read(&net_sem);
/* Ensure there are no outstanding rcu callbacks using this
* network namespace.
@@ -543,8 +554,10 @@ static void cleanup_net(struct work_struct *work)
*/
void net_ns_barrier(void)
{
+ down_write(&net_sem);
mutex_lock(&net_mutex);
mutex_unlock(&net_mutex);
+ up_write(&net_sem);
}
EXPORT_SYMBOL(net_ns_barrier);
@@ -871,12 +884,12 @@ static int __init net_ns_init(void)
rcu_assign_pointer(init_net.gen, ng);
- mutex_lock(&net_mutex);
+ down_write(&net_sem);
if (setup_net(&init_net, &init_user_ns))
panic("Could not setup the initial network namespace");
init_net_initialized = true;
- mutex_unlock(&net_mutex);
+ up_write(&net_sem);
register_pernet_subsys(&net_ns_ops);
@@ -1016,9 +1029,9 @@ static void unregister_pernet_operations(struct pernet_operations *ops)
int register_pernet_subsys(struct pernet_operations *ops)
{
int error;
- mutex_lock(&net_mutex);
+ down_write(&net_sem);
error = register_pernet_operations(first_device, ops);
- mutex_unlock(&net_mutex);
+ up_write(&net_sem);
return error;
}
EXPORT_SYMBOL_GPL(register_pernet_subsys);
@@ -1034,9 +1047,9 @@ EXPORT_SYMBOL_GPL(register_pernet_subsys);
*/
void unregister_pernet_subsys(struct pernet_operations *ops)
{
- mutex_lock(&net_mutex);
+ down_write(&net_sem);
unregister_pernet_operations(ops);
- mutex_unlock(&net_mutex);
+ up_write(&net_sem);
}
EXPORT_SYMBOL_GPL(unregister_pernet_subsys);
@@ -1062,11 +1075,11 @@ EXPORT_SYMBOL_GPL(unregister_pernet_subsys);
int register_pernet_device(struct pernet_operations *ops)
{
int error;
- mutex_lock(&net_mutex);
+ down_write(&net_sem);
error = register_pernet_operations(&pernet_list, ops);
if (!error && (first_device == &pernet_list))
first_device = &ops->list;
- mutex_unlock(&net_mutex);
+ up_write(&net_sem);
return error;
}
EXPORT_SYMBOL_GPL(register_pernet_device);
@@ -1082,11 +1095,11 @@ EXPORT_SYMBOL_GPL(register_pernet_device);
*/
void unregister_pernet_device(struct pernet_operations *ops)
{
- mutex_lock(&net_mutex);
+ down_write(&net_sem);
if (&ops->list == first_device)
first_device = first_device->next;
unregister_pernet_operations(ops);
- mutex_unlock(&net_mutex);
+ up_write(&net_sem);
}
EXPORT_SYMBOL_GPL(unregister_pernet_device);
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index bc290413a49d..257e7bbaffba 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -454,11 +454,11 @@ static void rtnl_lock_unregistering_all(void)
void rtnl_link_unregister(struct rtnl_link_ops *ops)
{
/* Close the race with cleanup_net() */
- mutex_lock(&net_mutex);
+ down_write(&net_sem);
rtnl_lock_unregistering_all();
__rtnl_link_unregister(ops);
rtnl_unlock();
- mutex_unlock(&net_mutex);
+ up_write(&net_sem);
}
EXPORT_SYMBOL_GPL(rtnl_link_unregister);