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>

2 files changed, 7 insertions, 5 deletions

diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index e9ee9ad0a681..3573b4bf2fdf 100644
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h
@@ -35,7 +35,6 @@ extern int rtnl_trylock(void);
 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
diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 9158ec1ad06f..115b01b92f4d 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -60,8 +60,11 @@ struct net {
 
         struct list_head        list;           /* list of network namespaces */
         struct list_head        cleanup_list;   /* namespaces on death row */
-        struct list_head        exit_list;      /* Use only net_mutex */
-
+        struct list_head        exit_list;      /* To linked to call pernet exit
+                                                 * methods on dead net (net_sem
+                                                 * read locked), or to unregister
+                                                 * pernet ops (net_sem wr locked).
+                                                 */
         struct user_namespace   *user_ns;       /* Owning user namespace */
         struct ucounts          *ucounts;
         spinlock_t              nsid_lock;
@@ -89,7 +92,7 @@ struct net {
         /* core fib_rules */
         struct list_head        rules_ops;
 
-        struct list_head        fib_notifier_ops;  /* protected by net_mutex */
+        struct list_head        fib_notifier_ops;  /* protected by net_sem */
 
         struct net_device       *loopback_dev;          /* The loopback */
         struct netns_core       core;
@@ -316,7 +319,7 @@ struct pernet_operations {
         /*
          * Indicates above methods are allowed to be executed in parallel
          * with methods of any other pernet_operations, i.e. they are not
-         * need synchronization via net_mutex.
+         * need write locked net_sem.
          */
         bool async;
 };