netdev - [PATCH net-next] net: avoid quadratic behavior in netdev_wait_allrefs

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Message-Id: <20220218065430.2613262-1-eric.dumazet@gmail.com>
Date:   Thu, 17 Feb 2022 22:54:30 -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: avoid quadratic behavior in netdev_wait_allrefs_any()

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

If the list of devices has N elements, netdev_wait_allrefs_any()
is called N times, and linkwatch_forget_dev() is called N*(N-1)/2 times.

Fix this by calling linkwatch_forget_dev() only once per device.

Fixes: faab39f63c1f ("net: allow out-of-order netdev unregistration")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/core/dev.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 05fa867f18787e709dcaccfea1df350c424eff80..acd884910e12a040841e1e0525e0d4bc5e3ee799 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -9828,9 +9828,6 @@ static struct net_device *netdev_wait_allrefs_any(struct list_head *list)
 	struct net_device *dev;
 	int wait = 0;
 
-	list_for_each_entry(dev, list, todo_list)
-		linkwatch_forget_dev(dev);
-
 	rebroadcast_time = warning_time = jiffies;
 
 	list_for_each_entry(dev, list, todo_list)
@@ -9951,6 +9948,7 @@ void netdev_run_todo(void)
 		}
 
 		dev->reg_state = NETREG_UNREGISTERED;
+		linkwatch_forget_dev(dev);
 	}
 
 	while (!list_empty(&list)) {
-- 
2.35.1.265.g69c8d7142f-goog