target: Fall back to vzalloc upon ->sess_cmd_map kzalloc failure

This patch changes transport_alloc_session_tags() to fall back to
use vzalloc when kzalloc fails for big tag_num that end up generating
larger order allocations.

Also use is_vmalloc_addr() in transport_alloc_session_tags() failure
path, and normal transport_free_session() path to determine when
vfree() needs to be called instead of kfree().

v2 changes:
  - Use  __GFP_NOWARN | __GFP_REPEAT for sess_cmd_map kzalloc (mst)

Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Asias He <asias@redhat.com>
Cc: Kent Overstreet <kmo@daterainc.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_transport.c

@@ -236,16 +236,23 @@ int transport_alloc_session_tags(struct se_session *se_sess,
 {
 	int rc;
 
-	se_sess->sess_cmd_map = kzalloc(tag_num * tag_size, GFP_KERNEL);
+	se_sess->sess_cmd_map = kzalloc(tag_num * tag_size,
+					GFP_KERNEL | __GFP_NOWARN | __GFP_REPEAT);
+	if (!se_sess->sess_cmd_map) {
+		se_sess->sess_cmd_map = vzalloc(tag_num * tag_size);
 		if (!se_sess->sess_cmd_map) {
 			pr_err("Unable to allocate se_sess->sess_cmd_map\n");
 			return -ENOMEM;
 		}
+	}
 
 	rc = percpu_ida_init(&se_sess->sess_tag_pool, tag_num);
 	if (rc < 0) {
 		pr_err("Unable to init se_sess->sess_tag_pool,"
 			" tag_num: %u\n", tag_num);
+		if (is_vmalloc_addr(se_sess->sess_cmd_map))
+			vfree(se_sess->sess_cmd_map);
+		else
 			kfree(se_sess->sess_cmd_map);
 		se_sess->sess_cmd_map = NULL;
 		return -ENOMEM;
@@ -412,6 +419,9 @@ void transport_free_session(struct se_session *se_sess)
 {
 	if (se_sess->sess_cmd_map) {
 		percpu_ida_destroy(&se_sess->sess_tag_pool);
+		if (is_vmalloc_addr(se_sess->sess_cmd_map))
+			vfree(se_sess->sess_cmd_map);
+		else
 			kfree(se_sess->sess_cmd_map);
 	}
 	kmem_cache_free(se_sess_cache, se_sess);