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Subject[PATCH v2 05/31] net: Allow pernet_operations to be executed in parallel
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This adds new pernet_operations::async flag to indicate operations,
which ->init(), ->exit() and ->exit_batch() methods are allowed
to be executed in parallel with the methods of any other pernet_operations.

When there are only asynchronous pernet_operations in the system,
net_mutex won't be taken for a net construction and destruction.

Also, remove BUG_ON(mutex_is_locked()) from net_assign_generic()
without replacing with the equivalent net_sem check, as there is
one more lockdep assert below.

Suggested-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
---
include/net/net_namespace.h | 6 ++++++
net/core/net_namespace.c | 29 +++++++++++++++++++----------
2 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 10f99dafd5ac..db978c4755f7 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -303,6 +303,12 @@ struct pernet_operations {
void (*exit_batch)(struct list_head *net_exit_list);
unsigned int *id;
size_t size;
+ /*
+ * Indicates above methods are allowe to be executed in parallel
+ * with methods of any other pernet_operations, i.e. they are not
+ * need synchronization via net_mutex.
+ */
+ bool async;
};

/*
diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index c4f7452906bb..550c766f73aa 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -41,8 +41,9 @@ struct net init_net = {
EXPORT_SYMBOL(init_net);

static bool init_net_initialized;
+static unsigned nr_sync_pernet_ops;
/*
- * net_sem: protects: pernet_list, net_generic_ids,
+ * net_sem: protects: pernet_list, net_generic_ids, nr_sync_pernet_ops,
* init_net_initialized and first_device pointer.
*/
DECLARE_RWSEM(net_sem);
@@ -70,11 +71,10 @@ static int net_assign_generic(struct net *net, unsigned int id, void *data)
{
struct net_generic *ng, *old_ng;

- BUG_ON(!mutex_is_locked(&net_mutex));
BUG_ON(id < MIN_PERNET_OPS_ID);

old_ng = rcu_dereference_protected(net->gen,
- lockdep_is_held(&net_mutex));
+ lockdep_is_held(&net_sem));
if (old_ng->s.len > id) {
old_ng->ptr[id] = data;
return 0;
@@ -419,11 +419,14 @@ struct net *copy_net_ns(unsigned long flags,
rv = down_read_killable(&net_sem);
if (rv < 0)
goto put_userns;
- rv = mutex_lock_killable(&net_mutex);
- if (rv < 0)
- goto up_read;
+ if (nr_sync_pernet_ops) {
+ rv = mutex_lock_killable(&net_mutex);
+ if (rv < 0)
+ goto up_read;
+ }
rv = setup_net(net, user_ns);
- mutex_unlock(&net_mutex);
+ if (nr_sync_pernet_ops)
+ mutex_unlock(&net_mutex);
up_read:
up_read(&net_sem);
if (rv < 0) {
@@ -453,7 +456,8 @@ static void cleanup_net(struct work_struct *work)
spin_unlock_irq(&cleanup_list_lock);

down_read(&net_sem);
- mutex_lock(&net_mutex);
+ if (nr_sync_pernet_ops)
+ mutex_lock(&net_mutex);

/* Don't let anyone else find us. */
rtnl_lock();
@@ -489,7 +493,8 @@ static void cleanup_net(struct work_struct *work)
list_for_each_entry_reverse(ops, &pernet_list, list)
ops_exit_list(ops, &net_exit_list);

- mutex_unlock(&net_mutex);
+ if (nr_sync_pernet_ops)
+ mutex_unlock(&net_mutex);

/* Free the net generic variables */
list_for_each_entry_reverse(ops, &pernet_list, list)
@@ -961,6 +966,9 @@ static int register_pernet_operations(struct list_head *list,
rcu_barrier();
if (ops->id)
ida_remove(&net_generic_ids, *ops->id);
+ } else if (!ops->async) {
+ pr_info_once("Pernet operations %ps are sync.\n", ops);
+ nr_sync_pernet_ops++;
}

return error;
@@ -968,7 +976,8 @@ static int register_pernet_operations(struct list_head *list,

static void unregister_pernet_operations(struct pernet_operations *ops)
{
-
+ if (!ops->async)
+ BUG_ON(nr_sync_pernet_ops-- == 0);
__unregister_pernet_operations(ops);
rcu_barrier();
if (ops->id)
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