mac80211: use RCU for TX aggregation

Currently we allocate some memory for each TX
aggregation session and additionally keep a
state bitmap indicating the state it is in.
By using RCU to protect the pointer, moving
the state into the structure and some locking
trickery we can avoid locking when the TX agg
session is fully operational.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 19 insertions, 14 deletions

diff --git a/net/mac80211/sta_info.h b/net/mac80211/sta_info.h
index 16864a6045b..05278e6288c 100644
--- a/net/mac80211/sta_info.h
+++ b/net/mac80211/sta_info.h
@@ -61,33 +61,40 @@ enum ieee80211_sta_info_flags {
 
 #define STA_TID_NUM 16
 #define ADDBA_RESP_INTERVAL HZ
-#define HT_AGG_MAX_RETRIES		(0x3)
+#define HT_AGG_MAX_RETRIES		0x3
 
-#define HT_AGG_STATE_INITIATOR_SHIFT	(4)
-
-#define HT_ADDBA_REQUESTED_MSK		BIT(0)
-#define HT_ADDBA_DRV_READY_MSK		BIT(1)
-#define HT_ADDBA_RECEIVED_MSK		BIT(2)
-#define HT_AGG_STATE_REQ_STOP_BA_MSK	BIT(3)
-#define HT_AGG_STATE_INITIATOR_MSK      BIT(HT_AGG_STATE_INITIATOR_SHIFT)
-#define HT_AGG_STATE_IDLE		(0x0)
-#define HT_AGG_STATE_OPERATIONAL	(HT_ADDBA_REQUESTED_MSK |	\
-					 HT_ADDBA_DRV_READY_MSK |	\
-					 HT_ADDBA_RECEIVED_MSK)
+#define HT_AGG_STATE_DRV_READY		0
+#define HT_AGG_STATE_RESPONSE_RECEIVED	1
+#define HT_AGG_STATE_OPERATIONAL	2
+#define HT_AGG_STATE_STOPPING		3
 
 /**
  * struct tid_ampdu_tx - TID aggregation information (Tx).
  *
+ * @rcu_head: rcu head for freeing structure
  * @addba_resp_timer: timer for peer's response to addba request
  * @pending: pending frames queue -- use sta's spinlock to protect
  * @ssn: Starting Sequence Number expected to be aggregated.
  * @dialog_token: dialog token for aggregation session
+ * @state: session state (see above)
+ * @stop_initiator: initiator of a session stop
+ *
+ * This structure is protected by RCU and the per-station
+ * spinlock. Assignments to the array holding it must hold
+ * the spinlock, only the TX path can access it under RCU
+ * lock-free if, and only if, the state has  the flag
+ * %HT_AGG_STATE_OPERATIONAL set. Otherwise, the TX path
+ * must also acquire the spinlock and re-check the state,
+ * see comments in the tx code touching it.
  */
 struct tid_ampdu_tx {
+	struct rcu_head rcu_head;
 	struct timer_list addba_resp_timer;
 	struct sk_buff_head pending;
+	unsigned long state;
 	u16 ssn;
 	u8 dialog_token;
+	u8 stop_initiator;
 };
 
 /**
@@ -129,7 +136,6 @@ struct tid_ampdu_rx {
  * struct sta_ampdu_mlme - STA aggregation information.
  *
  * @tid_rx: aggregation info for Rx per TID -- RCU protected
- * @tid_state_tx: TID's state in Tx session state machine.
  * @tid_tx: aggregation info for Tx per TID
  * @addba_req_num: number of times addBA request has been sent.
  * @dialog_token_allocator: dialog token enumerator for each new session;
@@ -138,7 +144,6 @@ struct sta_ampdu_mlme {
 	/* rx */
 	struct tid_ampdu_rx *tid_rx[STA_TID_NUM];
 	/* tx */
-	u8 tid_state_tx[STA_TID_NUM];
 	struct tid_ampdu_tx *tid_tx[STA_TID_NUM];
 	u8 addba_req_num[STA_TID_NUM];
 	u8 dialog_token_allocator;