mac80211: only set CSA beacon when at least one beacon must be transmitted

A beacon should never have a Channel Switch Announcement information
element with a count of 0, because a count of 1 means switch just
before the next beacon.  So, if a count of 0 was valid in a beacon, it
would have been transmitted in the next channel already, which is
useless.  A CSA count equal to zero is only meaningful in action
frames or probe_responses.

Fix the ieee80211_csa_is_complete() and ieee80211_update_csa()
functions accordingly.

With a CSA count of 0, we won't transmit any CSA beacons, because the
switch will happen before the next TBTT.  To avoid extra work and
potential confusion in the drivers, complete the CSA immediately,
instead of waiting for the driver to call ieee80211_csa_finish().

To keep things simpler, we also switch immediately when the CSA count
is 1, while in theory we should delay the switch until just before the
next TBTT.

Additionally, move the ieee80211_csa_finish() function to cfg.c,
where it makes more sense.

Tested-by: Simon Wunderlich <sw@simonwunderlich.de>
Acked-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Luciano Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 85 insertions, 30 deletions

diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index f111f8df4e65..032081c4cc65 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -2988,28 +2988,26 @@ cfg80211_beacon_dup(struct cfg80211_beacon_data *beacon)
         return new_beacon;
 }
 
-void ieee80211_csa_finalize_work(struct work_struct *work)
+void ieee80211_csa_finish(struct ieee80211_vif *vif)
 {
-        struct ieee80211_sub_if_data *sdata =
-                container_of(work, struct ieee80211_sub_if_data,
-                             csa_finalize_work);
-        struct ieee80211_local *local = sdata->local;
-        int err, changed = 0;
+        struct ieee80211_sub_if_data *sdata = vif_to_sdata(vif);
 
-        sdata_lock(sdata);
-        /* AP might have been stopped while waiting for the lock. */
-        if (!sdata->vif.csa_active)
-                goto unlock;
+        ieee80211_queue_work(&sdata->local->hw,
+                             &sdata->csa_finalize_work);
+}
+EXPORT_SYMBOL(ieee80211_csa_finish);
 
-        if (!ieee80211_sdata_running(sdata))
-                goto unlock;
+static void ieee80211_csa_finalize(struct ieee80211_sub_if_data *sdata)
+{
+        struct ieee80211_local *local = sdata->local;
+        int err, changed = 0;
 
         sdata->radar_required = sdata->csa_radar_required;
         mutex_lock(&local->mtx);
         err = ieee80211_vif_change_channel(sdata, &changed);
         mutex_unlock(&local->mtx);
         if (WARN_ON(err < 0))
-                goto unlock;
+                return;
 
         if (!local->use_chanctx) {
                 local->_oper_chandef = sdata->csa_chandef;
@@ -3023,7 +3021,7 @@ void ieee80211_csa_finalize_work(struct work_struct *work)
         case NL80211_IFTYPE_AP:
                 err = ieee80211_assign_beacon(sdata, sdata->u.ap.next_beacon);
                 if (err < 0)
-                        goto unlock;
+                        return;
 
                 changed |= err;
                 kfree(sdata->u.ap.next_beacon);
@@ -3038,12 +3036,12 @@ void ieee80211_csa_finalize_work(struct work_struct *work)
         case NL80211_IFTYPE_MESH_POINT:
                 err = ieee80211_mesh_finish_csa(sdata);
                 if (err < 0)
-                        goto unlock;
+                        return;
                 break;
 #endif
         default:
                 WARN_ON(1);
-                goto unlock;
+                return;
         }
 
         ieee80211_wake_queues_by_reason(&sdata->local->hw,
@@ -3051,6 +3049,23 @@ void ieee80211_csa_finalize_work(struct work_struct *work)
                                         IEEE80211_QUEUE_STOP_REASON_CSA);
 
         cfg80211_ch_switch_notify(sdata->dev, &sdata->csa_chandef);
+}
+
+void ieee80211_csa_finalize_work(struct work_struct *work)
+{
+        struct ieee80211_sub_if_data *sdata =
+                container_of(work, struct ieee80211_sub_if_data,
+                             csa_finalize_work);
+
+        sdata_lock(sdata);
+        /* AP might have been stopped while waiting for the lock. */
+        if (!sdata->vif.csa_active)
+                goto unlock;
+
+        if (!ieee80211_sdata_running(sdata))
+                goto unlock;
+
+        ieee80211_csa_finalize(sdata);
 
 unlock:
         sdata_unlock(sdata);
@@ -3064,7 +3079,7 @@ int ieee80211_channel_switch(struct wiphy *wiphy, struct net_device *dev,
         struct ieee80211_chanctx_conf *chanctx_conf;
         struct ieee80211_chanctx *chanctx;
         struct ieee80211_if_mesh __maybe_unused *ifmsh;
-        int err, num_chanctx;
+        int err, num_chanctx, changed = 0;
 
         lockdep_assert_held(&sdata->wdev.mtx);
 
@@ -3105,19 +3120,40 @@ int ieee80211_channel_switch(struct wiphy *wiphy, struct net_device *dev,
 
         switch (sdata->vif.type) {
         case NL80211_IFTYPE_AP:
-                sdata->csa_counter_offset_beacon =
-                        params->counter_offset_beacon;
-                sdata->csa_counter_offset_presp = params->counter_offset_presp;
                 sdata->u.ap.next_beacon =
                         cfg80211_beacon_dup(&params->beacon_after);
                 if (!sdata->u.ap.next_beacon)
                         return -ENOMEM;
 
+                /*
+                 * With a count of 0, we don't have to wait for any
+                 * TBTT before switching, so complete the CSA
+                 * immediately.  In theory, with a count == 1 we
+                 * should delay the switch until just before the next
+                 * TBTT, but that would complicate things so we switch
+                 * immediately too.  If we would delay the switch
+                 * until the next TBTT, we would have to set the probe
+                 * response here.
+                 *
+                 * TODO: A channel switch with count <= 1 without
+                 * sending a CSA action frame is kind of useless,
+                 * because the clients won't know we're changing
+                 * channels.  The action frame must be implemented
+                 * either here or in the userspace.
+                 */
+                if (params->count <= 1)
+                        break;
+
+                sdata->csa_counter_offset_beacon =
+                        params->counter_offset_beacon;
+                sdata->csa_counter_offset_presp = params->counter_offset_presp;
                 err = ieee80211_assign_beacon(sdata, &params->beacon_csa);
                 if (err < 0) {
                         kfree(sdata->u.ap.next_beacon);
                         return err;
                 }
+                changed |= err;
+
                 break;
         case NL80211_IFTYPE_ADHOC:
                 if (!sdata->vif.bss_conf.ibss_joined)
@@ -3145,9 +3181,16 @@ int ieee80211_channel_switch(struct wiphy *wiphy, struct net_device *dev,
                     params->chandef.chan->band)
                         return -EINVAL;
 
-                err = ieee80211_ibss_csa_beacon(sdata, params);
-                if (err < 0)
-                        return err;
+                /* see comments in the NL80211_IFTYPE_AP block */
+                if (params->count > 1) {
+                        err = ieee80211_ibss_csa_beacon(sdata, params);
+                        if (err < 0)
+                                return err;
+                        changed |= err;
+                }
+
+                ieee80211_send_action_csa(sdata, params);
+
                 break;
 #ifdef CONFIG_MAC80211_MESH
         case NL80211_IFTYPE_MESH_POINT:
@@ -3172,12 +3215,19 @@ int ieee80211_channel_switch(struct wiphy *wiphy, struct net_device *dev,
                 if (ifmsh->csa_role == IEEE80211_MESH_CSA_ROLE_NONE)
                         ifmsh->csa_role = IEEE80211_MESH_CSA_ROLE_INIT;
 
-                err = ieee80211_mesh_csa_beacon(sdata, params,
-                        (ifmsh->csa_role == IEEE80211_MESH_CSA_ROLE_INIT));
-                if (err < 0) {
-                        ifmsh->csa_role = IEEE80211_MESH_CSA_ROLE_NONE;
-                        return err;
+                /* see comments in the NL80211_IFTYPE_AP block */
+                if (params->count > 1) {
+                        err = ieee80211_mesh_csa_beacon(sdata, params);
+                        if (err < 0) {
+                                ifmsh->csa_role = IEEE80211_MESH_CSA_ROLE_NONE;
+                                return err;
+                        }
+                        changed |= err;
                 }
+
+                if (ifmsh->csa_role == IEEE80211_MESH_CSA_ROLE_INIT)
+                        ieee80211_send_action_csa(sdata, params);
+
                 break;
 #endif
         default:
@@ -3194,8 +3244,13 @@ int ieee80211_channel_switch(struct wiphy *wiphy, struct net_device *dev,
         sdata->csa_chandef = params->chandef;
         sdata->vif.csa_active = true;
 
-        ieee80211_bss_info_change_notify(sdata, err);
-        drv_channel_switch_beacon(sdata, &params->chandef);
+        if (changed) {
+                ieee80211_bss_info_change_notify(sdata, changed);
+                drv_channel_switch_beacon(sdata, &params->chandef);
+        } else {
+                /* if the beacon didn't change, we can finalize immediately */
+                ieee80211_csa_finalize(sdata);
+        }
 
         return 0;
 }