From 0b5c21bbc01e92745ca1ca4f6fd87d878fa3ea5e Mon Sep 17 00:00:00 2001 From: Johannes Berg Date: Mon, 4 Apr 2022 11:38:47 +0200 Subject: net: ensure net_todo_list is processed quickly In [1], Will raised a potential issue that the cfg80211 code, which does (from a locking perspective) rtnl_lock() wiphy_lock() rtnl_unlock() might be suspectible to ABBA deadlocks, because rtnl_unlock() calls netdev_run_todo(), which might end up calling rtnl_lock() again, which could then deadlock (see the comment in the code added here for the scenario). Some back and forth and thinking ensued, but clearly this can't happen if the net_todo_list is empty at the rtnl_unlock() here. Clearly, the code here cannot actually put an entry on it, and all other users of rtnl_unlock() will empty it since that will always go through netdev_run_todo(), emptying the list. So the only other way to get there would be to add to the list and then unlock the RTNL without going through rtnl_unlock(), which is only possible through __rtnl_unlock(). However, this isn't exported and not used in many places, and none of them seem to be able to unregister before using it. Therefore, add a WARN_ON() in the code to ensure this invariant won't be broken, so that the cfg80211 (or any similar) code stays safe. [1] https://lore.kernel.org/r/Yjzpo3TfZxtKPMAG@google.com Signed-off-by: Johannes Berg Link: https://lore.kernel.org/r/20220404113847.0ee02e4a70da.Ic73d206e217db20fd22dcec14fe5442ca732804b@changeid Signed-off-by: Jakub Kicinski --- include/linux/netdevice.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'include') diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index 59e27a2b7bf0..b6a1e7f643da 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -3894,7 +3894,8 @@ void dev_queue_xmit_nit(struct sk_buff *skb, struct net_device *dev); extern int netdev_budget; extern unsigned int netdev_budget_usecs; -/* Called by rtnetlink.c:rtnl_unlock() */ +/* Used by rtnetlink.c:__rtnl_unlock()/rtnl_unlock() */ +extern struct list_head net_todo_list; void netdev_run_todo(void); static inline void __dev_put(struct net_device *dev) -- cgit v1.2.3