[Devel] [PATCH RHEL7 COMMIT] net: Kill net_mutex

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-1127.8.2.vz7.161.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1127.8.2.vz7.161.3
------>
commit 39fb6f9def2c24896bbec28b039c4c8476c3332a
Author: Kirill Tkhai <ktkhai at virtuozzo.com>
Date:   Wed May 27 21:35:02 2020 +0300

    net: Kill net_mutex
    
    ms commit 19efbd93e6fb
    
    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 at virtuozzo.com>
    
    Signed-off-by: David S. Miller <davem at davemloft.net>
    [vz7: many intermediate and following patches skipped]
    Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
    
    =====================
    Patchset description:
    
    Parallel per-net init/exit
    
    https://jira.sw.ru/browse/PSBM-104158
---
 net/core/net_namespace.c | 11 +----------
 1 file changed, 1 insertion(+), 10 deletions(-)

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 9827efc52a2e6..c766e74c0fc55 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -31,7 +31,6 @@
 
 static LIST_HEAD(pernet_list);
 static struct list_head *first_device = &pernet_list;
-DEFINE_MUTEX(net_mutex);
 /*
  * net_sem: protects: pernet_list, net_generic_ids,
  * init_net_initialized and first_device pointer.
@@ -72,11 +71,10 @@ int net_assign_generic(struct net *net, int id, void *data)
 {
 	struct net_generic *ng, *old_ng;
 
-	BUG_ON(!mutex_is_locked(&net_mutex));
 	BUG_ON(id == 0);
 
 	old_ng = rcu_dereference_protected(net->gen,
-					   lockdep_is_held(&net_mutex));
+					   lockdep_is_held(&net_sem));
 	ng = old_ng;
 	if (old_ng->len >= id)
 		goto assign;
@@ -430,13 +428,7 @@ struct net *copy_net_ns(unsigned long flags,
 	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:
@@ -494,7 +486,6 @@ static void cleanup_net(struct work_struct *work)
 	spin_unlock_irq(&cleanup_list_lock);
 
 	down_read(&net_sem);
-	mutex_lock(&net_mutex);
 
 	/* Don't let anyone else find us. */
 	rtnl_lock();