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, 12 insertions, 26 deletions

diff --git a/net/mac80211/sta_info.h b/net/mac80211/sta_info.h
index 248f56e..97f25b9 100644
--- a/net/mac80211/sta_info.h
+++ b/net/mac80211/sta_info.h
@@ -16,6 +16,7 @@
 #include <linux/workqueue.h>
 #include <linux/average.h>
 #include <linux/etherdevice.h>
+#include <linux/rhashtable.h>
 #include "key.h"
 
 /**
@@ -246,7 +247,7 @@ struct sta_ampdu_mlme {
  *
  * @list: global linked list entry
  * @free_list: list entry for keeping track of stations to free
- * @hnext: hash table linked list pointer
+ * @hash_node: hash node for rhashtable
  * @local: pointer to the global information
  * @sdata: virtual interface this station belongs to
  * @ptk: peer keys negotiated with this station, if any
@@ -339,7 +340,7 @@ struct sta_info {
 	/* General information, mostly static */
 	struct list_head list, free_list;
 	struct rcu_head rcu_head;
-	struct sta_info __rcu *hnext;
+	struct rhash_head hash_node;
 	struct ieee80211_local *local;
 	struct ieee80211_sub_if_data *sdata;
 	struct ieee80211_key __rcu *gtk[NUM_DEFAULT_KEYS + NUM_DEFAULT_MGMT_KEYS];
@@ -535,10 +536,6 @@ rcu_dereference_protected_tid_tx(struct sta_info *sta, int tid)
 					 lockdep_is_held(&sta->ampdu_mlme.mtx));
 }
 
-#define STA_HASH_SIZE 256
-#define STA_HASH(sta) (sta[5])
-
-
 /* Maximum number of frames to buffer per power saving station per AC */
 #define STA_MAX_TX_BUFFER	64
 
@@ -559,26 +556,15 @@ struct sta_info *sta_info_get(struct ieee80211_sub_if_data *sdata,
 struct sta_info *sta_info_get_bss(struct ieee80211_sub_if_data *sdata,
 				  const u8 *addr);
 
-static inline
-void for_each_sta_info_type_check(struct ieee80211_local *local,
-				  const u8 *addr,
-				  struct sta_info *sta,
-				  struct sta_info *nxt)
-{
-}
+u32 sta_addr_hash(const void *key, u32 length, u32 seed);
+
+#define _sta_bucket_idx(_tbl, _a)					\
+	rht_bucket_index(_tbl, sta_addr_hash(_a, ETH_ALEN, (_tbl)->hash_rnd))
 
-#define for_each_sta_info(local, _addr, _sta, nxt)			\
-	for (	/* initialise loop */					\
-		_sta = rcu_dereference(local->sta_hash[STA_HASH(_addr)]),\
-		nxt = _sta ? rcu_dereference(_sta->hnext) : NULL;	\
-		/* typecheck */						\
-		for_each_sta_info_type_check(local, (_addr), _sta, nxt),\
-		/* continue condition */				\
-		_sta;							\
-		/* advance loop */					\
-		_sta = nxt,						\
-		nxt = _sta ? rcu_dereference(_sta->hnext) : NULL	\
-	     )								\
+#define for_each_sta_info(local, tbl, _addr, _sta, _tmp)		\
+	rht_for_each_entry_rcu(_sta, _tmp, tbl, 			\
+			       _sta_bucket_idx(tbl, _addr),		\
+			       hash_node)				\
 	/* compare address and run code only if it matches */		\
 	if (ether_addr_equal(_sta->sta.addr, (_addr)))
 
@@ -615,7 +601,7 @@ int sta_info_destroy_addr_bss(struct ieee80211_sub_if_data *sdata,
 
 void sta_info_recalc_tim(struct sta_info *sta);
 
-void sta_info_init(struct ieee80211_local *local);
+int sta_info_init(struct ieee80211_local *local);
 void sta_info_stop(struct ieee80211_local *local);
 
 /**