mac80211: Move num_sta_ps counter decrement after synchronize_rcu

Unted the assumption that the sta struct is still accessible before the
synchronize_rcu call we should move the num_sta_ps counter decrement
after synchronize_rcu to avoid incorrect decrements if num_sta_ps.
Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/sta_info.c

@@ -750,15 +750,6 @@ int __must_check __sta_info_destroy(struct sta_info *sta)
 
 	sta->dead = true;
 
-	if (test_sta_flag(sta, WLAN_STA_PS_STA)) {
-		BUG_ON(!sdata->bss);
-
-		clear_sta_flag(sta, WLAN_STA_PS_STA);
-
-		atomic_dec(&sdata->bss->num_sta_ps);
-		sta_info_recalc_tim(sta);
-	}
-
 	local->num_sta--;
 	local->sta_generation++;
 
@@ -790,6 +781,15 @@ int __must_check __sta_info_destroy(struct sta_info *sta)
 	 */
 	synchronize_rcu();
 
+	if (test_sta_flag(sta, WLAN_STA_PS_STA)) {
+		BUG_ON(!sdata->bss);
+
+		clear_sta_flag(sta, WLAN_STA_PS_STA);
+
+		atomic_dec(&sdata->bss->num_sta_ps);
+		sta_info_recalc_tim(sta);
+	}
+
 	for (ac = 0; ac < IEEE80211_NUM_ACS; ac++) {
 		local->total_ps_buffered -= skb_queue_len(&sta->ps_tx_buf[ac]);
 		__skb_queue_purge(&sta->ps_tx_buf[ac]);