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, 2 insertions, 2 deletions

diff --git a/net/rds/stats.c b/net/rds/stats.c
index c66d95d9c26..b77be8be33b 100644
--- a/net/rds/stats.c
+++ b/net/rds/stats.c
@@ -57,8 +57,8 @@ static const char *const rds_stat_names[] = {
         "recv_ping",
         "send_queue_empty",
         "send_queue_full",
-        "send_sem_contention",
-        "send_sem_queue_raced",
+        "send_lock_contention",
+        "send_lock_queue_raced",
         "send_immediate_retry",
         "send_delayed_retry",
         "send_drop_acked",