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, 6 insertions, 16 deletions

diff --git a/net/rds/connection.c b/net/rds/connection.c
index 88bcaf3f3e1..56aebe444ad 100644
--- a/net/rds/connection.c
+++ b/net/rds/connection.c
@@ -62,18 +62,6 @@ static struct hlist_head *rds_conn_bucket(__be32 laddr, __be32 faddr)
                 var |= RDS_INFO_CONNECTION_FLAG_##suffix;       \
 } while (0)
 
-static inline int rds_conn_is_sending(struct rds_connection *conn)
-{
-        int ret = 0;
-
-        if (!mutex_trylock(&conn->c_send_lock))
-                ret = 1;
-        else
-                mutex_unlock(&conn->c_send_lock);
-
-        return ret;
-}
-
 static struct rds_connection *rds_conn_lookup(struct hlist_head *head,
                                               __be32 laddr, __be32 faddr,
                                               struct rds_transport *trans)
@@ -158,7 +146,7 @@ static struct rds_connection *__rds_conn_create(__be32 laddr, __be32 faddr,
         spin_lock_init(&conn->c_lock);
         conn->c_next_tx_seq = 1;
 
-        mutex_init(&conn->c_send_lock);
+        spin_lock_init(&conn->c_send_lock);
         INIT_LIST_HEAD(&conn->c_send_queue);
         INIT_LIST_HEAD(&conn->c_retrans);
 
@@ -283,10 +271,12 @@ void rds_conn_shutdown(struct rds_connection *conn)
                 }
                 mutex_unlock(&conn->c_cm_lock);
 
-                mutex_lock(&conn->c_send_lock);
+                /* verify everybody's out of rds_send_xmit() */
+                spin_lock_irq(&conn->c_send_lock);
+                spin_unlock_irq(&conn->c_send_lock);
+
                 conn->c_trans->conn_shutdown(conn);
                 rds_conn_reset(conn);
-                mutex_unlock(&conn->c_send_lock);
 
                 if (!rds_conn_transition(conn, RDS_CONN_DISCONNECTING, RDS_CONN_DOWN)) {
                         /* This can happen - eg when we're in the middle of tearing
@@ -476,7 +466,7 @@ static int rds_conn_info_visitor(struct rds_connection *conn,
         cinfo->flags = 0;
 
         rds_conn_info_set(cinfo->flags,
-                          rds_conn_is_sending(conn), SENDING);
+                          spin_is_locked(&conn->c_send_lock), SENDING);
         /* XXX Future: return the state rather than these funky bits */
         rds_conn_info_set(cinfo->flags,
                           atomic_read(&conn->c_state) == RDS_CONN_CONNECTING,