mac80211: fix spurious RCU warning and update documentation

Document rx vs tx status concurrency requirements.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/net/mac80211/rate.c b/net/mac80211/rate.c
index 0d51877efdb7..d3f414fe67e0 100644
--- a/net/mac80211/rate.c
+++ b/net/mac80211/rate.c
@@ -688,8 +688,15 @@ int rate_control_set_rates(struct ieee80211_hw *hw,
                            struct ieee80211_sta *pubsta,
                            struct ieee80211_sta_rates *rates)
 {
-        struct ieee80211_sta_rates *old = rcu_dereference(pubsta->rates);
+        struct ieee80211_sta_rates *old;
 
+        /*
+         * mac80211 guarantees that this function will not be called
+         * concurrently, so the following RCU access is safe, even without
+         * extra locking. This can not be checked easily, so we just set
+         * the condition to true.
+         */
+        old = rcu_dereference_protected(pubsta->rates, true);
         rcu_assign_pointer(pubsta->rates, rates);
         if (old)
                 kfree_rcu(old, rcu_head);