cfg80211: change netdev registration/unregistration semantics

We used to not require anything in terms of registering netdevs
with cfg80211, using a netdev notifier instead. However, in the
next patch reducing RTNL locking, this causes big problems, and
the simplest way is to just require drivers to do things better.

Change the registration/unregistration semantics to require the
drivers to call cfg80211_(un)register_netdevice() when this is
happening due to a cfg80211 request, i.e. add_virtual_intf() or
del_virtual_intf() (or if it somehow has to happen in any other
cfg80211 callback).

Otherwise, in other contexts, drivers may continue to use the
normal netdev (un)registration functions as usual.

Internally, we still use the netdev notifier and track (by the
new wdev->registered bool) if the wdev had already been added
to cfg80211 or not.

Link: https://lore.kernel.org/r/20210122161942.cf2f4b65e4e9.Ida8234e50da13eb675b557bac52a713ad4eddf71@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 32 insertions, 8 deletions

diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
index 798f8eb15e00..e7703fdbac8d 100644
--- a/include/net/cfg80211.h
+++ b/include/net/cfg80211.h
@@ -5228,6 +5228,7 @@ struct cfg80211_cqm_config;
  *
  * @wiphy: pointer to hardware description
  * @iftype: interface type
+ * @registered: is this wdev already registered with cfg80211
  * @list: (private) Used to collect the interfaces
  * @netdev: (private) Used to reference back to the netdev, may be %NULL
  * @identifier: (private) Identifier used in nl80211 to identify this
@@ -5311,7 +5312,7 @@ struct wireless_dev {
 
 	struct mutex mtx;
 
-	bool use_4addr, is_running;
+	bool use_4addr, is_running, registered;
 
 	u8 address[ETH_ALEN] __aligned(sizeof(u16));
 
@@ -7654,19 +7655,42 @@ u32 cfg80211_calculate_bitrate(struct rate_info *rate);
  * cfg80211_unregister_wdev - remove the given wdev
  * @wdev: struct wireless_dev to remove
  *
- * Call this function only for wdevs that have no netdev assigned,
- * e.g. P2P Devices. It removes the device from the list so that
- * it can no longer be used. It is necessary to call this function
- * even when cfg80211 requests the removal of the interface by
- * calling the del_virtual_intf() callback. The function must also
- * be called when the driver wishes to unregister the wdev, e.g.
- * when the device is unbound from the driver.
+ * This function removes the device so it can no longer be used. It is necessary
+ * to call this function even when cfg80211 requests the removal of the device
+ * by calling the del_virtual_intf() callback. The function must also be called
+ * when the driver wishes to unregister the wdev, e.g. when the hardware device
+ * is unbound from the driver.
  *
  * Requires the RTNL to be held.
  */
 void cfg80211_unregister_wdev(struct wireless_dev *wdev);
 
 /**
+ * cfg80211_register_netdevice - register the given netdev
+ * @dev: the netdev to register
+ *
+ * Note: In contexts coming from cfg80211 callbacks, you must call this rather
+ * than register_netdevice(), unregister_netdev() is impossible as the RTNL is
+ * held. Otherwise, both register_netdevice() and register_netdev() are usable
+ * instead as well.
+ */
+int cfg80211_register_netdevice(struct net_device *dev);
+
+/**
+ * cfg80211_unregister_netdevice - unregister the given netdev
+ * @dev: the netdev to register
+ *
+ * Note: In contexts coming from cfg80211 callbacks, you must call this rather
+ * than unregister_netdevice(), unregister_netdev() is impossible as the RTNL
+ * is held. Otherwise, both unregister_netdevice() and unregister_netdev() are
+ * usable instead as well.
+ */
+static inline void cfg80211_unregister_netdevice(struct net_device *dev)
+{
+	cfg80211_unregister_wdev(dev->ieee80211_ptr);
+}
+
+/**
  * struct cfg80211_ft_event_params - FT Information Elements
  * @ies: FT IEs
  * @ies_len: length of the FT IE in bytes