mac80211: update mesh beacon on workqueue

Instead of updating the mesh beacon immediately when
requested (which would require the sdata_lock()), defer it
to the mac80211 workqueue.

Fixes yet another deadlock on calling sta_info_flush()
with the sdata_lock() held from ieee80211_stop_mesh(). We
could just drop the sdata_lock() around the
mesh_sta_cleanup() call, but this path is also taken from
several non-locked error paths.

Signed-off-by: Thomas Pedersen <[e-mail]>
[fix comment position]
Signed-off-by: Johannes Berg <[e-mail]>

net/mac80211/ieee80211_i.h

···
 	struct timer_list mesh_path_root_timer;
 
 	unsigned long wrkq_flags;
+	unsigned long mbss_changed;
 
 	u8 mesh_id[IEEE80211_MAX_MESH_ID_LEN];
 	size_t mesh_id_len;

net/mac80211/mesh.c

···
 		del_timer_sync(&sta->plink_timer);
 	}
 
-	if (changed) {
-		sdata_lock(sdata);
+	if (changed)
 		ieee80211_mbss_info_change_notify(sdata, changed);
-		sdata_unlock(sdata);
-	}
 }
 
 int mesh_rmc_init(struct ieee80211_sub_if_data *sdata)
···
 void ieee80211_mbss_info_change_notify(struct ieee80211_sub_if_data *sdata,
 				       u32 changed)
 {
-	if (sdata->vif.bss_conf.enable_beacon &&
-	    (changed & (BSS_CHANGED_BEACON |
-			BSS_CHANGED_HT |
-			BSS_CHANGED_BASIC_RATES |
-			BSS_CHANGED_BEACON_INT)))
-		if (ieee80211_mesh_rebuild_beacon(sdata))
-			return;
-	ieee80211_bss_info_change_notify(sdata, changed);
+	struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
+	unsigned long bits = changed;
+	u32 bit;
+
+	if (!bits)
+		return;
+
+	/* if we race with running work, worst case this work becomes a noop */
+	for_each_set_bit(bit, &bits, sizeof(changed) * BITS_PER_BYTE)
+		set_bit(bit, &ifmsh->mbss_changed);
+	set_bit(MESH_WORK_MBSS_CHANGED, &ifmsh->wrkq_flags);
+	ieee80211_queue_work(&sdata->local->hw, &sdata->work);
 }
 
 int ieee80211_start_mesh(struct ieee80211_sub_if_data *sdata)
···
 	del_timer_sync(&sdata->u.mesh.housekeeping_timer);
 	del_timer_sync(&sdata->u.mesh.mesh_path_root_timer);
 	del_timer_sync(&sdata->u.mesh.mesh_path_timer);
+
+	/* clear any mesh work (for next join) we may have accrued */
+	ifmsh->wrkq_flags = 0;
+	ifmsh->mbss_changed = 0;
 
 	local->fif_other_bss--;
 	atomic_dec(&local->iff_allmultis);
···
 	sdata_unlock(sdata);
 }
 
+static void mesh_bss_info_changed(struct ieee80211_sub_if_data *sdata)
+{
+	struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
+	u32 bit, changed = 0;
+
+	for_each_set_bit(bit, &ifmsh->mbss_changed,
+			 sizeof(changed) * BITS_PER_BYTE) {
+		clear_bit(bit, &ifmsh->mbss_changed);
+		changed |= BIT(bit);
+	}
+
+	if (sdata->vif.bss_conf.enable_beacon &&
+	    (changed & (BSS_CHANGED_BEACON |
+			BSS_CHANGED_HT |
+			BSS_CHANGED_BASIC_RATES |
+			BSS_CHANGED_BEACON_INT)))
+		if (ieee80211_mesh_rebuild_beacon(sdata))
+			return;
+
+	ieee80211_bss_info_change_notify(sdata, changed);
+}
+
 void ieee80211_mesh_work(struct ieee80211_sub_if_data *sdata)
 {
 	struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
···
 	if (test_and_clear_bit(MESH_WORK_DRIFT_ADJUST, &ifmsh->wrkq_flags))
 		mesh_sync_adjust_tbtt(sdata);
 
+	if (test_and_clear_bit(MESH_WORK_MBSS_CHANGED, &ifmsh->wrkq_flags))
+		mesh_bss_info_changed(sdata);
 out:
 	sdata_unlock(sdata);
 }

net/mac80211/mesh.h

···
  * @MESH_WORK_ROOT: the mesh root station needs to send a frame
  * @MESH_WORK_DRIFT_ADJUST: time to compensate for clock drift relative to other
  * mesh nodes
+ * @MESH_WORK_MBSS_CHANGED: rebuild beacon and notify driver of BSS changes
  */
 enum mesh_deferred_task_flags {
 	MESH_WORK_HOUSEKEEPING,
···
 	MESH_WORK_GROW_MPP_TABLE,
 	MESH_WORK_ROOT,
 	MESH_WORK_DRIFT_ADJUST,
+	MESH_WORK_MBSS_CHANGED,
 };
 
 /**