mac80211: use rhashtable for station table

We currently have a hand-rolled table with 256 entries and are
using the last byte of the MAC address as the hash. This hash
is obviously very fast, but collisions are easily created and
we waste a lot of space in the common case of just connecting
as a client to an AP where we just have a single station. The
other common case of an AP is also suboptimal due to the size
of the hash table and the ease of causing collisions.

Convert all of this to use rhashtable with jhash, which gives
us the advantage of a far better hash function (with random
perturbation to avoid hash collision attacks) and of course
that the hash table grows and shrinks dynamically with chain
length, improving both cases above.

Use a specialised hash function (using jhash, but with fixed
length) to achieve better compiler optimisation as suggested
by Sergey Ryazanov.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 52 insertions, 51 deletions

diff --git a/net/mac80211/sta_info.c b/net/mac80211/sta_info.c
index aacaa1a85e63..81cc499fa4a9 100644
--- a/net/mac80211/sta_info.c
+++ b/net/mac80211/sta_info.c
@@ -64,32 +64,20 @@
  * freed before they are done using it.
  */
 
+static const struct rhashtable_params sta_rht_params = {
+	.nelem_hint = 3, /* start small */
+	.head_offset = offsetof(struct sta_info, hash_node),
+	.key_offset = offsetof(struct sta_info, sta.addr),
+	.key_len = ETH_ALEN,
+	.hashfn = sta_addr_hash,
+};
+
 /* Caller must hold local->sta_mtx */
 static int sta_info_hash_del(struct ieee80211_local *local,
 			     struct sta_info *sta)
 {
-	struct sta_info *s;
-
-	s = rcu_dereference_protected(local->sta_hash[STA_HASH(sta->sta.addr)],
-				      lockdep_is_held(&local->sta_mtx));
-	if (!s)
-		return -ENOENT;
-	if (s == sta) {
-		rcu_assign_pointer(local->sta_hash[STA_HASH(sta->sta.addr)],
-				   s->hnext);
-		return 0;
-	}
-
-	while (rcu_access_pointer(s->hnext) &&
-	       rcu_access_pointer(s->hnext) != sta)
-		s = rcu_dereference_protected(s->hnext,
-					lockdep_is_held(&local->sta_mtx));
-	if (rcu_access_pointer(s->hnext)) {
-		rcu_assign_pointer(s->hnext, sta->hnext);
-		return 0;
-	}
-
-	return -ENOENT;
+	return rhashtable_remove_fast(&local->sta_hash, &sta->hash_node,
+				      sta_rht_params);
 }
 
 static void __cleanup_single_sta(struct sta_info *sta)
@@ -159,18 +147,8 @@ struct sta_info *sta_info_get(struct ieee80211_sub_if_data *sdata,
 			      const u8 *addr)
 {
 	struct ieee80211_local *local = sdata->local;
-	struct sta_info *sta;
 
-	sta = rcu_dereference_check(local->sta_hash[STA_HASH(addr)],
-				    lockdep_is_held(&local->sta_mtx));
-	while (sta) {
-		if (sta->sdata == sdata &&
-		    ether_addr_equal(sta->sta.addr, addr))
-			break;
-		sta = rcu_dereference_check(sta->hnext,
-					    lockdep_is_held(&local->sta_mtx));
-	}
-	return sta;
+	return rhashtable_lookup_fast(&local->sta_hash, addr, sta_rht_params);
 }
 
 /*
@@ -182,18 +160,24 @@ struct sta_info *sta_info_get_bss(struct ieee80211_sub_if_data *sdata,
 {
 	struct ieee80211_local *local = sdata->local;
 	struct sta_info *sta;
+	struct rhash_head *tmp;
+	const struct bucket_table *tbl;
 
-	sta = rcu_dereference_check(local->sta_hash[STA_HASH(addr)],
-				    lockdep_is_held(&local->sta_mtx));
-	while (sta) {
-		if ((sta->sdata == sdata ||
-		     (sta->sdata->bss && sta->sdata->bss == sdata->bss)) &&
-		    ether_addr_equal(sta->sta.addr, addr))
-			break;
-		sta = rcu_dereference_check(sta->hnext,
-					    lockdep_is_held(&local->sta_mtx));
+	rcu_read_lock();
+	tbl = rht_dereference_rcu(local->sta_hash.tbl, &local->sta_hash);
+
+	for_each_sta_info(local, tbl, addr, sta, tmp) {
+		if (sta->sdata == sdata ||
+		    (sta->sdata->bss && sta->sdata->bss == sdata->bss)) {
+			rcu_read_unlock();
+			/* this is safe as the caller must already hold
+			 * another rcu read section or the mutex
+			 */
+			return sta;
+		}
 	}
-	return sta;
+	rcu_read_unlock();
+	return NULL;
 }
 
 struct sta_info *sta_info_get_by_idx(struct ieee80211_sub_if_data *sdata,
@@ -242,9 +226,8 @@ void sta_info_free(struct ieee80211_local *local, struct sta_info *sta)
 static void sta_info_hash_add(struct ieee80211_local *local,
 			      struct sta_info *sta)
 {
-	lockdep_assert_held(&local->sta_mtx);
-	sta->hnext = local->sta_hash[STA_HASH(sta->sta.addr)];
-	rcu_assign_pointer(local->sta_hash[STA_HASH(sta->sta.addr)], sta);
+	rhashtable_insert_fast(&local->sta_hash, &sta->hash_node,
+			       sta_rht_params);
 }
 
 static void sta_deliver_ps_frames(struct work_struct *wk)
@@ -948,19 +931,32 @@ static void sta_info_cleanup(unsigned long data)
 		  round_jiffies(jiffies + STA_INFO_CLEANUP_INTERVAL));
 }
 
-void sta_info_init(struct ieee80211_local *local)
+u32 sta_addr_hash(const void *key, u32 length, u32 seed)
+{
+	return jhash(key, ETH_ALEN, seed);
+}
+
+int sta_info_init(struct ieee80211_local *local)
 {
+	int err;
+
+	err = rhashtable_init(&local->sta_hash, &sta_rht_params);
+	if (err)
+		return err;
+
 	spin_lock_init(&local->tim_lock);
 	mutex_init(&local->sta_mtx);
 	INIT_LIST_HEAD(&local->sta_list);
 
 	setup_timer(&local->sta_cleanup, sta_info_cleanup,
 		    (unsigned long)local);
+	return 0;
 }
 
 void sta_info_stop(struct ieee80211_local *local)
 {
 	del_timer_sync(&local->sta_cleanup);
+	rhashtable_destroy(&local->sta_hash);
 }
 
 
@@ -1024,16 +1020,21 @@ void ieee80211_sta_expire(struct ieee80211_sub_if_data *sdata,
 }
 
 struct ieee80211_sta *ieee80211_find_sta_by_ifaddr(struct ieee80211_hw *hw,
-					       const u8 *addr,
-					       const u8 *localaddr)
+						   const u8 *addr,
+						   const u8 *localaddr)
 {
-	struct sta_info *sta, *nxt;
+	struct ieee80211_local *local = hw_to_local(hw);
+	struct sta_info *sta;
+	struct rhash_head *tmp;
+	const struct bucket_table *tbl;
+
+	tbl = rht_dereference_rcu(local->sta_hash.tbl, &local->sta_hash);
 
 	/*
 	 * Just return a random station if localaddr is NULL
 	 * ... first in list.
 	 */
-	for_each_sta_info(hw_to_local(hw), addr, sta, nxt) {
+	for_each_sta_info(local, tbl, addr, sta, tmp) {
 		if (localaddr &&
 		    !ether_addr_equal(sta->sdata->vif.addr, localaddr))
 			continue;