netdev - [PATCH v3 net-next 5/5] net: reduce RTNL hold duration in unregister_netdevice_many

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250114205531.967841-6-edumazet@google.com>
Date: Tue, 14 Jan 2025 20:55:31 +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 v3 net-next 5/5] 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 <edumazet@...gle.com>
---
 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 574bd40f3a2bfcc6e43300fad669b1579d48039a..0bb97bb392dcdfa82292fe1ae2ee8290b036df60 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -11601,9 +11601,8 @@ 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;
-- 
2.48.0.rc2.279.g1de40edade-goog