netdev - [PATCH net-next 3/4] net: expedite synchronize_net() for cleanup

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Message-ID: <20250107173838.1130187-4-edumazet@google.com>
Date: Tue,  7 Jan 2025 17:38:37 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, Simon Horman <horms@...nel.org>, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 3/4] net: expedite synchronize_net() for cleanup_net()

cleanup_net() is the single thread responsible
for netns dismantles, and a potential bottleneck.

Before we can get per-netns RTNL, make sure
all synchronize_net() called from this thread
are using rcu_synchronize_expedited().

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/net/net_namespace.h | 2 ++
 net/core/dev.c              | 2 +-
 net/core/net_namespace.c    | 5 +++++
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 5a2a0df8ad91b677b515b392869c6c755be5c868..a3009bdd7efec0a3b665cbf51c159c323458410a 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -565,4 +565,6 @@ void net_ns_init(void);
 static inline void net_ns_init(void) {}
 #endif
 
+extern struct task_struct *cleanup_net_task;
+
 #endif /* __NET_NET_NAMESPACE_H */
diff --git a/net/core/dev.c b/net/core/dev.c
index ef6426aad84dc00740a1716c8fd4cfd48ee17cf3..342ab7d6001da8983db450f50327fc7915b0a8ba 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -11423,7 +11423,7 @@ EXPORT_SYMBOL_GPL(alloc_netdev_dummy);
 void synchronize_net(void)
 {
 	might_sleep();
-	if (rtnl_is_locked())
+	if (current == cleanup_net_task || rtnl_is_locked())
 		synchronize_rcu_expedited();
 	else
 		synchronize_rcu();
diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index b5cd3ae4f04cf28d43f8401a3dafebac4a297123..cb39a12b2f8295c605f08b5589932932150a1644 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -588,6 +588,8 @@ static void unhash_nsid(struct net *net, struct net *last)
 
 static LLIST_HEAD(cleanup_list);
 
+struct task_struct *cleanup_net_task;
+
 static void cleanup_net(struct work_struct *work)
 {
 	const struct pernet_operations *ops;
@@ -596,6 +598,8 @@ static void cleanup_net(struct work_struct *work)
 	LIST_HEAD(net_exit_list);
 	LIST_HEAD(dev_kill_list);
 
+	cleanup_net_task = current;
+
 	/* Atomically snapshot the list of namespaces to cleanup */
 	net_kill_list = llist_del_all(&cleanup_list);
 
@@ -670,6 +674,7 @@ static void cleanup_net(struct work_struct *work)
 		put_user_ns(net->user_ns);
 		net_free(net);
 	}
+	cleanup_net_task = NULL;
 }
 
 /**
-- 
2.47.1.613.gc27f4b7a9f-goog