RDS: Change send lock from a mutex to a spinlock

This change allows us to call rds_send_xmit() from a tasklet,
which is crucial to our new operating model.

* Change c_send_lock to a spinlock
* Update stats fields "sem_" to "_lock"
* Remove unneeded rds_conn_is_sending()

About locking between shutdown and send -- send checks if the
connection is up. Shutdown puts the connection into
DISCONNECTING. After this, all threads entering send will exit
immediately. However, a thread could be *in* send_xmit(), so
shutdown acquires the c_send_lock to ensure everyone is out
before proceeding with connection shutdown.

Signed-off-by: Andy Grover <andy.grover@oracle.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/net/rds/rds.h b/net/rds/rds.h
index e81d7e4..c3a668b 100644
--- a/net/rds/rds.h
+++ b/net/rds/rds.h
@@ -91,7 +91,7 @@ struct rds_connection {
 	struct rds_cong_map	*c_lcong;
 	struct rds_cong_map	*c_fcong;
 
-	struct mutex		c_send_lock;	/* protect send ring */
+	spinlock_t		c_send_lock;	/* protect send ring */
 	struct rds_message	*c_xmit_rm;
 	unsigned long		c_xmit_sg;
 	unsigned int		c_xmit_hdr_off;
@@ -548,8 +548,8 @@ struct rds_statistics {
 	uint64_t	s_recv_ping;
 	uint64_t	s_send_queue_empty;
 	uint64_t	s_send_queue_full;
-	uint64_t	s_send_sem_contention;
-	uint64_t	s_send_sem_queue_raced;
+	uint64_t	s_send_lock_contention;
+	uint64_t	s_send_lock_queue_raced;
 	uint64_t	s_send_immediate_retry;
 	uint64_t	s_send_delayed_retry;
 	uint64_t	s_send_drop_acked;