mac80211: fix station destruction in AP/mesh modes

Unfortunately, commit b22cfcfcae5b, intended to speed up roaming
by avoiding the synchronize_rcu() broke AP/mesh modes as it moved
some code into that work item that will still call into the driver
at a time where it's no longer expected to handle this: after the
AP or mesh has been stopped.

To fix this problem remove the per-station work struct, maintain a
station cleanup list instead and flush this list when stations are
flushed. To keep this patch smaller for stable, do this when the
stations are flushed (sta_info_flush()). This unfortunately brings
back the original roaming delay; I'll fix that again in a separate
patch.

Also, Ben reported that the original commit could sometimes (with
many interfaces) cause long delays when an interface is set down,
due to blocking on flush_workqueue(). Since we now maintain the
cleanup list, this particular change of the original patch can be
reverted.

Cc: stable@vger.kernel.org [3.7]
Reported-by: Ben Greear <greearb@candelatech.com>
Tested-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

4 files changed, 62 insertions, 17 deletions

diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index 28fc9875537c..2fcd274877d7 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -773,6 +773,10 @@ struct ieee80211_sub_if_data {
                 u32 mntr_flags;
         } u;
 
+        spinlock_t cleanup_stations_lock;
+        struct list_head cleanup_stations;
+        struct work_struct cleanup_stations_wk;
+
 #ifdef CONFIG_MAC80211_DEBUGFS
         struct {
                 struct dentry *dir;
diff --git a/net/mac80211/iface.c b/net/mac80211/iface.c
index 54fb7f9db564..0f2a9f987f79 100644
--- a/net/mac80211/iface.c
+++ b/net/mac80211/iface.c
@@ -868,20 +868,11 @@ static void ieee80211_do_stop(struct ieee80211_sub_if_data *sdata,
                 cancel_work_sync(&sdata->work);
                 /*
                  * When we get here, the interface is marked down.
-                 * Call rcu_barrier() to wait both for the RX path
+                 * Call synchronize_rcu() to wait for the RX path
                  * should it be using the interface and enqueuing
-                 * frames at this very time on another CPU, and
-                 * for the sta free call_rcu callbacks.
+                 * frames at this very time on another CPU.
                  */
-                rcu_barrier();
-
-                /*
-                 * free_sta_rcu() enqueues a work for the actual
-                 * sta cleanup, so we need to flush it while
-                 * sdata is still valid.
-                 */
-                flush_workqueue(local->workqueue);
-
+                synchronize_rcu();
                 skb_queue_purge(&sdata->skb_queue);
 
                 /*
@@ -1501,6 +1492,15 @@ static void ieee80211_assign_perm_addr(struct ieee80211_local *local,
         mutex_unlock(&local->iflist_mtx);
 }
 
+static void ieee80211_cleanup_sdata_stas_wk(struct work_struct *wk)
+{
+        struct ieee80211_sub_if_data *sdata;
+
+        sdata = container_of(wk, struct ieee80211_sub_if_data, cleanup_stations_wk);
+
+        ieee80211_cleanup_sdata_stas(sdata);
+}
+
 int ieee80211_if_add(struct ieee80211_local *local, const char *name,
                      struct wireless_dev **new_wdev, enum nl80211_iftype type,
                      struct vif_params *params)
@@ -1576,6 +1576,10 @@ int ieee80211_if_add(struct ieee80211_local *local, const char *name,
 
         INIT_LIST_HEAD(&sdata->key_list);
 
+        spin_lock_init(&sdata->cleanup_stations_lock);
+        INIT_LIST_HEAD(&sdata->cleanup_stations);
+        INIT_WORK(&sdata->cleanup_stations_wk, ieee80211_cleanup_sdata_stas_wk);
+
         for (i = 0; i < IEEE80211_NUM_BANDS; i++) {
                 struct ieee80211_supported_band *sband;
                 sband = local->hw.wiphy->bands[i];
diff --git a/net/mac80211/sta_info.c b/net/mac80211/sta_info.c
index f3e502502fee..8bbd3b0fdbcc 100644
--- a/net/mac80211/sta_info.c
+++ b/net/mac80211/sta_info.c
@@ -91,9 +91,8 @@ static int sta_info_hash_del(struct ieee80211_local *local,
         return -ENOENT;
 }
 
-static void free_sta_work(struct work_struct *wk)
+static void cleanup_single_sta(struct sta_info *sta)
 {
-        struct sta_info *sta = container_of(wk, struct sta_info, free_sta_wk);
         int ac, i;
         struct tid_ampdu_tx *tid_tx;
         struct ieee80211_sub_if_data *sdata = sta->sdata;
@@ -153,11 +152,35 @@ static void free_sta_work(struct work_struct *wk)
         sta_info_free(local, sta);
 }
 
+void ieee80211_cleanup_sdata_stas(struct ieee80211_sub_if_data *sdata)
+{
+        struct sta_info *sta;
+
+        spin_lock_bh(&sdata->cleanup_stations_lock);
+        while (!list_empty(&sdata->cleanup_stations)) {
+                sta = list_first_entry(&sdata->cleanup_stations,
+                                       struct sta_info, list);
+                list_del(&sta->list);
+                spin_unlock_bh(&sdata->cleanup_stations_lock);
+
+                cleanup_single_sta(sta);
+
+                spin_lock_bh(&sdata->cleanup_stations_lock);
+        }
+
+        spin_unlock_bh(&sdata->cleanup_stations_lock);
+}
+
 static void free_sta_rcu(struct rcu_head *h)
 {
         struct sta_info *sta = container_of(h, struct sta_info, rcu_head);
+        struct ieee80211_sub_if_data *sdata = sta->sdata;
 
-        ieee80211_queue_work(&sta->local->hw, &sta->free_sta_wk);
+        spin_lock(&sdata->cleanup_stations_lock);
+        list_add_tail(&sta->list, &sdata->cleanup_stations);
+        spin_unlock(&sdata->cleanup_stations_lock);
+
+        ieee80211_queue_work(&sdata->local->hw, &sdata->cleanup_stations_wk);
 }
 
 /* protected by RCU */
@@ -310,7 +333,6 @@ struct sta_info *sta_info_alloc(struct ieee80211_sub_if_data *sdata,
 
         spin_lock_init(&sta->lock);
         INIT_WORK(&sta->drv_unblock_wk, sta_unblock);
-        INIT_WORK(&sta->free_sta_wk, free_sta_work);
         INIT_WORK(&sta->ampdu_mlme.work, ieee80211_ba_session_work);
         mutex_init(&sta->ampdu_mlme.mtx);
 
@@ -891,6 +913,20 @@ int sta_info_flush(struct ieee80211_local *local,
         }
         mutex_unlock(&local->sta_mtx);
 
+        rcu_barrier();
+
+        if (sdata) {
+                ieee80211_cleanup_sdata_stas(sdata);
+                cancel_work_sync(&sdata->cleanup_stations_wk);
+        } else {
+                mutex_lock(&local->iflist_mtx);
+                list_for_each_entry(sdata, &local->interfaces, list) {
+                        ieee80211_cleanup_sdata_stas(sdata);
+                        cancel_work_sync(&sdata->cleanup_stations_wk);
+                }
+                mutex_unlock(&local->iflist_mtx);
+        }
+
         return ret;
 }
 
diff --git a/net/mac80211/sta_info.h b/net/mac80211/sta_info.h
index 1489bca9ea97..37c1889afd3a 100644
--- a/net/mac80211/sta_info.h
+++ b/net/mac80211/sta_info.h
@@ -299,7 +299,6 @@ struct sta_info {
         spinlock_t lock;
 
         struct work_struct drv_unblock_wk;
-        struct work_struct free_sta_wk;
 
         u16 listen_interval;
 
@@ -563,4 +562,6 @@ void ieee80211_sta_ps_deliver_wakeup(struct sta_info *sta);
 void ieee80211_sta_ps_deliver_poll_response(struct sta_info *sta);
 void ieee80211_sta_ps_deliver_uapsd(struct sta_info *sta);
 
+void ieee80211_cleanup_sdata_stas(struct ieee80211_sub_if_data *sdata);
+
 #endif /* STA_INFO_H */