net: Kill net_mutex
We take net_mutex, when there are !async pernet_operations
registered, and read locking of net_sem is not enough. But
we may get rid of taking the mutex, and just change the logic
to write lock net_sem in such cases. This obviously reduces
the number of lock operations, we do.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index bcab9a9..e89a516 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -29,8 +29,6 @@
static LIST_HEAD(pernet_list);
static struct list_head *first_device = &pernet_list;
-/* Used only if there are !async pernet_operations registered */
-DEFINE_MUTEX(net_mutex);
LIST_HEAD(net_namespace_list);
EXPORT_SYMBOL_GPL(net_namespace_list);
@@ -407,6 +405,7 @@ struct net *copy_net_ns(unsigned long flags,
{
struct ucounts *ucounts;
struct net *net;
+ unsigned write;
int rv;
if (!(flags & CLONE_NEWNET))
@@ -424,20 +423,26 @@ struct net *copy_net_ns(unsigned long flags,
refcount_set(&net->passive, 1);
net->ucounts = ucounts;
get_user_ns(user_ns);
-
- rv = down_read_killable(&net_sem);
+again:
+ write = READ_ONCE(nr_sync_pernet_ops);
+ if (write)
+ rv = down_write_killable(&net_sem);
+ else
+ rv = down_read_killable(&net_sem);
if (rv < 0)
goto put_userns;
- if (nr_sync_pernet_ops) {
- rv = mutex_lock_killable(&net_mutex);
- if (rv < 0)
- goto up_read;
+
+ if (!write && unlikely(READ_ONCE(nr_sync_pernet_ops))) {
+ up_read(&net_sem);
+ goto again;
}
rv = setup_net(net, user_ns);
- if (nr_sync_pernet_ops)
- mutex_unlock(&net_mutex);
-up_read:
- up_read(&net_sem);
+
+ if (write)
+ up_write(&net_sem);
+ else
+ up_read(&net_sem);
+
if (rv < 0) {
put_userns:
put_user_ns(user_ns);
@@ -485,15 +490,23 @@ static void cleanup_net(struct work_struct *work)
struct net *net, *tmp, *last;
struct list_head net_kill_list;
LIST_HEAD(net_exit_list);
+ unsigned write;
/* Atomically snapshot the list of namespaces to cleanup */
spin_lock_irq(&cleanup_list_lock);
list_replace_init(&cleanup_list, &net_kill_list);
spin_unlock_irq(&cleanup_list_lock);
+again:
+ write = READ_ONCE(nr_sync_pernet_ops);
+ if (write)
+ down_write(&net_sem);
+ else
+ down_read(&net_sem);
- down_read(&net_sem);
- if (nr_sync_pernet_ops)
- mutex_lock(&net_mutex);
+ if (!write && unlikely(READ_ONCE(nr_sync_pernet_ops))) {
+ up_read(&net_sem);
+ goto again;
+ }
/* Don't let anyone else find us. */
rtnl_lock();
@@ -528,14 +541,14 @@ static void cleanup_net(struct work_struct *work)
list_for_each_entry_reverse(ops, &pernet_list, list)
ops_exit_list(ops, &net_exit_list);
- if (nr_sync_pernet_ops)
- mutex_unlock(&net_mutex);
-
/* Free the net generic variables */
list_for_each_entry_reverse(ops, &pernet_list, list)
ops_free_list(ops, &net_exit_list);
- up_read(&net_sem);
+ if (write)
+ up_write(&net_sem);
+ else
+ up_read(&net_sem);
/* Ensure there are no outstanding rcu callbacks using this
* network namespace.
@@ -563,8 +576,6 @@ 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);