mac80211: Avoid filling up mesh preq queue with redundant requests

Don't accept redundant PREQs for a given destination. This fixes a
problem under high load:

kernel: [20386.250913] mesh_queue_preq: 235 callbacks suppressed
kernel: [20386.253335] Mesh HWMP (mesh0): PREQ node queue full
kernel: [20386.253352] Mesh HWMP (mesh0): PREQ node queue full
(...)

The 802.11s protocol has a provision to limit the rate of path requests
(PREQs) are transmitted (dot11MeshHWMPpreqMinInterval) but there was no
limit on the rate at which PREQs were being queued up.  There is a valid
reason for queuing PREQs: this way we can even out PREQ bursts.  But
queueing multiple PREQs for the same destination is useless.

Reported-by: Pedro Larbig <pedro.larbig@carhs.de>
Signed-off-by: Javier Cardona <javier@cozybit.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 13 insertions, 2 deletions

diff --git a/net/mac80211/mesh_hwmp.c b/net/mac80211/mesh_hwmp.c
index 9a1f8bbc49b8..b22b223ccde1 100644
--- a/net/mac80211/mesh_hwmp.c
+++ b/net/mac80211/mesh_hwmp.c
@@ -867,9 +867,19 @@ static void mesh_queue_preq(struct mesh_path *mpath, u8 flags)
                 return;
         }
 
+        spin_lock_bh(&mpath->state_lock);
+        if (mpath->flags & MESH_PATH_REQ_QUEUED) {
+                spin_unlock_bh(&mpath->state_lock);
+                spin_unlock_bh(&ifmsh->mesh_preq_queue_lock);
+                return;
+        }
+
         memcpy(preq_node->dst, mpath->dst, ETH_ALEN);
         preq_node->flags = flags;
 
+        mpath->flags |= MESH_PATH_REQ_QUEUED;
+        spin_unlock_bh(&mpath->state_lock);
+
         list_add_tail(&preq_node->list, &ifmsh->preq_queue.list);
         ++ifmsh->preq_queue_len;
         spin_unlock_bh(&ifmsh->mesh_preq_queue_lock);
@@ -921,6 +931,7 @@ void mesh_path_start_discovery(struct ieee80211_sub_if_data *sdata)
                 goto enddiscovery;
 
         spin_lock_bh(&mpath->state_lock);
+        mpath->flags &= ~MESH_PATH_REQ_QUEUED;
         if (preq_node->flags & PREQ_Q_F_START) {
                 if (mpath->flags & MESH_PATH_RESOLVING) {
                         spin_unlock_bh(&mpath->state_lock);
@@ -1028,8 +1039,7 @@ int mesh_nexthop_lookup(struct sk_buff *skb,
                         mesh_queue_preq(mpath, PREQ_Q_F_START);
                 }
 
-                if (skb_queue_len(&mpath->frame_queue) >=
-                                MESH_FRAME_QUEUE_LEN)
+                if (skb_queue_len(&mpath->frame_queue) >= MESH_FRAME_QUEUE_LEN)
                         skb_to_free = skb_dequeue(&mpath->frame_queue);
 
                 info->flags |= IEEE80211_TX_INTFL_NEED_TXPROCESSING;
@@ -1061,6 +1071,7 @@ void mesh_path_timer(unsigned long data)
         } else if (mpath->discovery_retries < max_preq_retries(sdata)) {
                 ++mpath->discovery_retries;
                 mpath->discovery_timeout *= 2;
+                mpath->flags &= ~MESH_PATH_REQ_QUEUED;
                 spin_unlock_bh(&mpath->state_lock);
                 mesh_queue_preq(mpath, 0);
         } else {