mac80211: Add stations iterator where the iterator function may sleep

ieee80211_iterate_active_interfaces() and
ieee80211_iterate_active_interfaces_atomic() already exist, where the
former allows the iterator function to sleep. Add
ieee80211_iterate_stations() which is similar to
ieee80211_iterate_stations_atomic() but allows the iterator to sleep.
This is needed for adding SDIO support to the rtw88 driver. Some
interators there are reading or writing registers. With the SDIO ops
(sdio_readb, sdio_writeb and friends) this means that the iterator
function may sleep.
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Link: https://lore.kernel.org/r/20211228211501.468981-2-martin.blumenstingl@googlemail.comSigned-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/mac80211.h

@@ -5614,6 +5614,9 @@ void ieee80211_iterate_active_interfaces_atomic(struct ieee80211_hw *hw,
  * This function iterates over the interfaces associated with a given
  * hardware that are currently active and calls the callback for them.
  * This version can only be used while holding the wiphy mutex.
+ * The driver must not call this with a lock held that it can also take in
+ * response to callbacks from mac80211, and it must not call this within
+ * callbacks made by mac80211 - both would result in deadlocks.
  *
  * @hw: the hardware struct of which the interfaces should be iterated over
  * @iter_flags: iteration flags, see &enum ieee80211_interface_iteration_flags
@@ -5627,6 +5630,24 @@ void ieee80211_iterate_active_interfaces_mtx(struct ieee80211_hw *hw,
 						struct ieee80211_vif *vif),
 					     void *data);
 
+/**
+ * ieee80211_iterate_stations - iterate stations
+ *
+ * This function iterates over all stations associated with a given
+ * hardware that are currently uploaded to the driver and calls the callback
+ * function for them.
+ * This function allows the iterator function to sleep, when the iterator
+ * function is atomic @ieee80211_iterate_stations_atomic can be used.
+ *
+ * @hw: the hardware struct of which the interfaces should be iterated over
+ * @iterator: the iterator function to call, cannot sleep
+ * @data: first argument of the iterator function
+ */
+void ieee80211_iterate_stations(struct ieee80211_hw *hw,
+				void (*iterator)(void *data,
+						 struct ieee80211_sta *sta),
+				void *data);
+
 /**
  * ieee80211_iterate_stations_atomic - iterate stations
  *

net/mac80211/util.c

@@ -862,6 +862,19 @@ static void __iterate_stations(struct ieee80211_local *local,
 	}
 }
 
+void ieee80211_iterate_stations(struct ieee80211_hw *hw,
+				void (*iterator)(void *data,
+						 struct ieee80211_sta *sta),
+				void *data)
+{
+	struct ieee80211_local *local = hw_to_local(hw);
+
+	mutex_lock(&local->sta_mtx);
+	__iterate_stations(local, iterator, data);
+	mutex_unlock(&local->sta_mtx);
+}
+EXPORT_SYMBOL_GPL(ieee80211_iterate_stations);
+
 void ieee80211_iterate_stations_atomic(struct ieee80211_hw *hw,
 			void (*iterator)(void *data,
 					 struct ieee80211_sta *sta),