netdev - [PATCH net-next] net: make net->dev_unreg

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Date:   Wed,  9 Feb 2022 18:59:32 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH net-next] net: make net->dev_unreg_count atomic

From: Eric Dumazet <edumazet@...gle.com>

Having to acquire rtnl from netdev_run_todo() for every dismantled
device is not desirable when/if rtnl is under stress.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/net/net_namespace.h |  2 +-
 net/core/dev.c              | 11 ++++-------
 net/core/rtnetlink.c        |  2 +-
 3 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 374cc7b260fcdf15a8fc2c709d0b0fc6d99e8c5c..c4f5601f6e32aff401dfb462fb4949ec7d37833a 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -63,7 +63,7 @@ struct net {
 						 */
 	spinlock_t		rules_mod_lock;
 
-	unsigned int		dev_unreg_count;
+	atomic_t		dev_unreg_count;
 
 	unsigned int		dev_base_seq;	/* protected by rtnl_mutex */
 	int			ifindex;
diff --git a/net/core/dev.c b/net/core/dev.c
index f5ef5160108131de8892555d2c73e4adaf98eeed..2c3b8744e00c01448e8882460760fdb3304f0476 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -9143,7 +9143,7 @@ DECLARE_WAIT_QUEUE_HEAD(netdev_unregistering_wq);
 static void net_set_todo(struct net_device *dev)
 {
 	list_add_tail(&dev->todo_list, &net_todo_list);
-	dev_net(dev)->dev_unreg_count++;
+	atomic_inc(&dev_net(dev)->dev_unreg_count);
 }
 
 static netdev_features_t netdev_sync_upper_features(struct net_device *lower,
@@ -9965,11 +9965,8 @@ void netdev_run_todo(void)
 		if (dev->needs_free_netdev)
 			free_netdev(dev);
 
-		/* Report a network device has been unregistered */
-		rtnl_lock();
-		dev_net(dev)->dev_unreg_count--;
-		__rtnl_unlock();
-		wake_up(&netdev_unregistering_wq);
+		if (atomic_dec_and_test(&dev_net(dev)->dev_unreg_count))
+			wake_up(&netdev_unregistering_wq);
 
 		/* Free network device */
 		kobject_put(&dev->dev.kobj);
@@ -10898,7 +10895,7 @@ static void __net_exit rtnl_lock_unregistering(struct list_head *net_list)
 		unregistering = false;
 
 		list_for_each_entry(net, net_list, exit_list) {
-			if (net->dev_unreg_count > 0) {
+			if (atomic_read(&net->dev_unreg_count) > 0) {
 				unregistering = true;
 				break;
 			}
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 710da8a36729d6a9293b610b029bd33aa38d6514..a6fad3df42a800792ed362e7f75de20880c53726 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -459,7 +459,7 @@ static void rtnl_lock_unregistering_all(void)
 		 * setup_net() and cleanup_net() are not possible.
 		 */
 		for_each_net(net) {
-			if (net->dev_unreg_count > 0) {
+			if (atomic_read(&net->dev_unreg_count) > 0) {
 				unregistering = true;
 				break;
 			}
-- 
2.35.0.263.gb82422642f-goog