target: Drop iSCSI use of mutex around max_cmd_sn increment

In a performance profile, taking a mutex in iscsit_increment_maxcmdsn()
shows up very high.  However taking a mutex around "sess->max_cmd_sn += 1"
seems pretty silly: we're not serializing against other contexts in
any useful way.

I did a quick audit and there don't appear to be any other places that
use max_cmd_sn within the mutex more than once, so this lock can't be
providing any useful serialization.

(Get correct values for logging - fix whitespace damage)

Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Spencer Baugh <sbaugh@catern.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/iscsi_target_nego.c

@@ -340,7 +340,6 @@ static int iscsi_target_check_first_request(
 static int iscsi_target_do_tx_login_io(struct iscsi_conn *conn, struct iscsi_login *login)
 {
 	u32 padding = 0;
-	struct iscsi_session *sess = conn->sess;
 	struct iscsi_login_rsp *login_rsp;
 
 	login_rsp = (struct iscsi_login_rsp *) login->rsp;
@@ -352,7 +351,7 @@ static int iscsi_target_do_tx_login_io(struct iscsi_conn *conn, struct iscsi_log
 	login_rsp->itt			= login->init_task_tag;
 	login_rsp->statsn		= cpu_to_be32(conn->stat_sn++);
 	login_rsp->exp_cmdsn		= cpu_to_be32(conn->sess->exp_cmd_sn);
-	login_rsp->max_cmdsn		= cpu_to_be32(conn->sess->max_cmd_sn);
+	login_rsp->max_cmdsn		= cpu_to_be32((u32) atomic_read(&conn->sess->max_cmd_sn));
 
 	pr_debug("Sending Login Response, Flags: 0x%02x, ITT: 0x%08x,"
 		" ExpCmdSN; 0x%08x, MaxCmdSN: 0x%08x, StatSN: 0x%08x, Length:"
@@ -367,10 +366,8 @@ static int iscsi_target_do_tx_login_io(struct iscsi_conn *conn, struct iscsi_log
 		return -1;
 
 	login->rsp_length		= 0;
-	mutex_lock(&sess->cmdsn_mutex);
-	login_rsp->exp_cmdsn		= cpu_to_be32(sess->exp_cmd_sn);
-	login_rsp->max_cmdsn		= cpu_to_be32(sess->max_cmd_sn);
-	mutex_unlock(&sess->cmdsn_mutex);
+	login_rsp->exp_cmdsn		= cpu_to_be32(login_rsp->exp_cmdsn);
+	login_rsp->max_cmdsn		= cpu_to_be32(login_rsp->max_cmdsn);
 
 	return 0;
 }