target/iscsi: Allocate session IDs from an IDA

Since the session is never looked up by ID, we can use the more
space-efficient IDA instead of the IDR.

Signed-off-by: Matthew Wilcox <willy@infradead.org>
diff --git a/drivers/target/iscsi/iscsi_target.c b/drivers/target/iscsi/iscsi_target.c
index 8e22379..94bad43 100644
--- a/drivers/target/iscsi/iscsi_target.c
+++ b/drivers/target/iscsi/iscsi_target.c
@@ -57,9 +57,8 @@
 static DEFINE_MUTEX(np_lock);
 
 static struct idr tiqn_idr;
-struct idr sess_idr;
+DEFINE_IDA(sess_ida);
 struct mutex auth_id_lock;
-spinlock_t sess_idr_lock;
 
 struct iscsit_global *iscsit_global;
 
@@ -700,9 +699,7 @@
 
 	spin_lock_init(&iscsit_global->ts_bitmap_lock);
 	mutex_init(&auth_id_lock);
-	spin_lock_init(&sess_idr_lock);
 	idr_init(&tiqn_idr);
-	idr_init(&sess_idr);
 
 	ret = target_register_template(&iscsi_ops);
 	if (ret)
@@ -4375,10 +4372,7 @@
 	pr_debug("Decremented number of active iSCSI Sessions on"
 		" iSCSI TPG: %hu to %u\n", tpg->tpgt, tpg->nsessions);
 
-	spin_lock(&sess_idr_lock);
-	idr_remove(&sess_idr, sess->session_index);
-	spin_unlock(&sess_idr_lock);
-
+	ida_free(&sess_ida, sess->session_index);
 	kfree(sess->sess_ops);
 	sess->sess_ops = NULL;
 	spin_unlock_bh(&se_tpg->session_lock);