mac80211: Fixing sparse warning at sta_info.c

The commit 42624d4913a00219a8fdbb4bafd634d1d843be85
created following sparse warning
>net/mac80211/sta_info.c:965:24: warning: incorrect type in assignment (different address spaces)
>net/mac80211/sta_info.c:965:24:    expected struct tid_ampdu_tx *tid_tx
>net/mac80211/sta_info.c:965:24:    got struct tid_ampdu_tx [noderef] <asn:4>*<noident>

Making use of rcu_dereference_protected to fix the problem.

V2:
 - Replacing rcu_dereference with rcu_dereference_protected
   as suggested by Johannes.
 - Adding mutex_lock/unlock to satisfy the condition at
   rcu_dereference_protected

Cc: Nishant Sarmukadam <nishants@marvell.com>
Reported-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Yogesh Ashok Powar <yogeshp@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/net/mac80211/sta_info.c b/net/mac80211/sta_info.c
index 2db01e9541e7..3d01abb2b813 100644
--- a/net/mac80211/sta_info.c
+++ b/net/mac80211/sta_info.c
@@ -822,10 +822,13 @@ static int __must_check __sta_info_destroy(struct sta_info *sta)
          * until the aggregation stop completes. Refer
          * http://thread.gmane.org/gmane.linux.kernel.wireless.general/81936
          */
+
+        mutex_lock(&sta->ampdu_mlme.mtx);
+
         for (i = 0; i < STA_TID_NUM; i++) {
-                if (!sta->ampdu_mlme.tid_tx[i])
+                tid_tx = rcu_dereference_protected_tid_tx(sta, i);
+                if (!tid_tx)
                         continue;
-                tid_tx = sta->ampdu_mlme.tid_tx[i];
                 if (skb_queue_len(&tid_tx->pending)) {
 #ifdef CONFIG_MAC80211_HT_DEBUG
                         wiphy_debug(local->hw.wiphy, "TX A-MPDU  purging %d "
@@ -837,6 +840,8 @@ static int __must_check __sta_info_destroy(struct sta_info *sta)
                 kfree_rcu(tid_tx, rcu_head);
         }
 
+        mutex_unlock(&sta->ampdu_mlme.mtx);
+
         sta_info_free(local, sta);
 
         return 0;