target: Fix max_cmd_sn increment w/o cmdsn mutex regressions

Current for-next iscsi target is broken:

commit 109e2381749c1cfd94a0d22b2b54142539024973
Author: Roland Dreier <roland@purestorage.com>
Date:   Thu Jul 23 14:53:32 2015 -0700

    target: Drop iSCSI use of mutex around max_cmd_sn increment

This patch fixes incorrect pr_debug() + atomic_inc_return() usage
within iscsit_increment_maxcmdsn() code.

Also fix funny iscsit_determine_maxcmdsn() usage and update
iscsi_target_do_tx_login_io() code.

Reported-by: Sagi Grimberg <sagig@mellanox.com>
Cc: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>
Cc: Roland Dreier <roland@purestorage.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/iscsi_target_device.c

@@ -47,16 +47,19 @@ void iscsit_determine_maxcmdsn(struct iscsi_session *sess)
 	 * core_set_queue_depth_for_node().
 	 */
 	sess->cmdsn_window = se_nacl->queue_depth;
-	atomic_set(&sess->max_cmd_sn, (u32) atomic_read(&sess->max_cmd_sn) + se_nacl->queue_depth - 1);
+	atomic_add(se_nacl->queue_depth - 1, &sess->max_cmd_sn);
 }
 
 void iscsit_increment_maxcmdsn(struct iscsi_cmd *cmd, struct iscsi_session *sess)
 {
+	u32 max_cmd_sn;
+
 	if (cmd->immediate_cmd || cmd->maxcmdsn_inc)
 		return;
 
 	cmd->maxcmdsn_inc = 1;
 
-	pr_debug("Updated MaxCmdSN to 0x%08x\n", atomic_inc_return(&sess->max_cmd_sn));
+	max_cmd_sn = atomic_inc_return(&sess->max_cmd_sn);
+	pr_debug("Updated MaxCmdSN to 0x%08x\n", max_cmd_sn);
 }
 EXPORT_SYMBOL(iscsit_increment_maxcmdsn);

drivers/target/iscsi/iscsi_target_nego.c

@@ -366,8 +366,6 @@ static int iscsi_target_do_tx_login_io(struct iscsi_conn *conn, struct iscsi_log
 		return -1;
 
 	login->rsp_length		= 0;
-	login_rsp->exp_cmdsn		= cpu_to_be32(login_rsp->exp_cmdsn);
-	login_rsp->max_cmdsn		= cpu_to_be32(login_rsp->max_cmdsn);
 
 	return 0;
 }