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>

1 files changed, 2 insertions, 5 deletions

diff --git a/drivers/target/iscsi/iscsi_target_device.c b/drivers/target/iscsi/iscsi_target_device.c
index 5fabcd3d623f..07d2ef67dba6 100644
--- a/drivers/target/iscsi/iscsi_target_device.c
+++ b/drivers/target/iscsi/iscsi_target_device.c
@@ -47,7 +47,7 @@ void iscsit_determine_maxcmdsn(struct iscsi_session *sess)
 	 * core_set_queue_depth_for_node().
 	 */
 	sess->cmdsn_window = se_nacl->queue_depth;
-	sess->max_cmd_sn = (sess->max_cmd_sn + se_nacl->queue_depth) - 1;
+	atomic_set(&sess->max_cmd_sn, (u32) atomic_read(&sess->max_cmd_sn) + se_nacl->queue_depth - 1);
 }
 
 void iscsit_increment_maxcmdsn(struct iscsi_cmd *cmd, struct iscsi_session *sess)
@@ -57,9 +57,6 @@ void iscsit_increment_maxcmdsn(struct iscsi_cmd *cmd, struct iscsi_session *sess
 
 	cmd->maxcmdsn_inc = 1;
 
-	mutex_lock(&sess->cmdsn_mutex);
-	sess->max_cmd_sn += 1;
-	pr_debug("Updated MaxCmdSN to 0x%08x\n", sess->max_cmd_sn);
-	mutex_unlock(&sess->cmdsn_mutex);
+	pr_debug("Updated MaxCmdSN to 0x%08x\n", atomic_inc_return(&sess->max_cmd_sn));
 }
 EXPORT_SYMBOL(iscsit_increment_maxcmdsn);