mac80211: Fix incorrect num_sta_ps decrement in ap_sta_ps_end

If the driver blocked this specific STA with the help of
ieee80211_sta_block_awake we won't clear WLAN_STA_PS_STA later but
still decrement num_sta_ps. Hence, the next data frame from this
STA will trigger ap_sta_ps_end again and also decrement num_sta_ps
again leading to an incorrect num_sta_ps counter.

This can result in problems with powersaving clients not waking up
from PS because the TIM calculation might be skipped due to the
incorrect num_sta_ps counter.

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/rx.c

@@ -1145,19 +1145,15 @@ static void ap_sta_ps_start(struct sta_info *sta)
 
 static void ap_sta_ps_end(struct sta_info *sta)
 {
-	struct ieee80211_sub_if_data *sdata = sta->sdata;
-
-	atomic_dec(&sdata->bss->num_sta_ps);
-
 #ifdef CONFIG_MAC80211_VERBOSE_PS_DEBUG
 	printk(KERN_DEBUG "%s: STA %pM aid %d exits power save mode\n",
-	       sdata->name, sta->sta.addr, sta->sta.aid);
+	       sta->sdata->name, sta->sta.addr, sta->sta.aid);
 #endif /* CONFIG_MAC80211_VERBOSE_PS_DEBUG */
 
 	if (test_sta_flag(sta, WLAN_STA_PS_DRIVER)) {
 #ifdef CONFIG_MAC80211_VERBOSE_PS_DEBUG
 		printk(KERN_DEBUG "%s: STA %pM aid %d driver-ps-blocked\n",
-		       sdata->name, sta->sta.addr, sta->sta.aid);
+		       sta->sdata->name, sta->sta.addr, sta->sta.aid);
 #endif /* CONFIG_MAC80211_VERBOSE_PS_DEBUG */
 		return;
 	}

net/mac80211/sta_info.c

@@ -997,9 +997,11 @@ EXPORT_SYMBOL(ieee80211_find_sta);
 static void clear_sta_ps_flags(void *_sta)
 {
 	struct sta_info *sta = _sta;
+	struct ieee80211_sub_if_data *sdata = sta->sdata;
 
 	clear_sta_flag(sta, WLAN_STA_PS_DRIVER);
-	clear_sta_flag(sta, WLAN_STA_PS_STA);
+	if (test_and_clear_sta_flag(sta, WLAN_STA_PS_STA))
+		atomic_dec(&sdata->bss->num_sta_ps);
 }
 
 /* powersave support code */