From 83419b61d187ce22aa3da5ffdda850fca3a12600 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 14 Jan 2025 20:55:31 +0000 Subject: [PATCH] net: reduce RTNL hold duration in unregister_netdevice_many_notify() (part 2) One synchronize_net() call is currently done while holding RTNL. This is source of RTNL contention in workloads adding and deleting many network namespaces per second, because synchronize_rcu() and synchronize_rcu_expedited() can use 60+ ms in some cases. For cleanup_net() use, temporarily release RTNL while calling the last synchronize_net(). This should be safe, because devices are no longer visible to other threads after unlist_netdevice() call and setting dev->reg_state to NETREG_UNREGISTERING. In any case, the new netdev_lock() / netdev_unlock() infrastructure that we are adding should allow to fix potential issues, with a combination of a per-device mutex and dev->reg_state awareness. Signed-off-by: Eric Dumazet Reviewed-by: Jesse Brandeburg Link: https://patch.msgid.link/20250114205531.967841-6-edumazet@google.com Signed-off-by: Jakub Kicinski --- net/core/dev.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/net/core/dev.c b/net/core/dev.c index 3924a4af68b81..3c87cb1cb8771 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -11628,9 +11628,8 @@ void unregister_netdevice_many_notify(struct list_head *head, rtnl_drop_if_cleanup_net(); flush_all_backlogs(); - rtnl_acquire_if_cleanup_net(); - /* TODO: move this before the prior rtnl_acquire_if_cleanup_net() */ synchronize_net(); + rtnl_acquire_if_cleanup_net(); list_for_each_entry(dev, head, unreg_list) { struct sk_buff *skb = NULL;