Patch "iscsi-target: Set session_fall_back_to_erl0 when forcing reinstatement" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

iscsi-target: Set session_fall_back_to_erl0 when forcing reinstatement

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
iscsi-target-set-session_fall_back_to_erl0-when-forcing-reinstatement.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Nicholas Bellinger <[email protected]>
Date: Tue, 25 Apr 2017 10:55:12 -0700
Subject: iscsi-target: Set session_fall_back_to_erl0 when forcing reinstatement

From: Nicholas Bellinger <[email protected]>

commit 197b806ae5db60c6f609d74da04ddb62ea5e1b00 upstream.

While testing modification of per se_node_acl queue_depth forcing session reinstatement via lio_target_nacl_cmdsn_depth_store() -> core_tpg_set_initiator_node_queue_depth(), a hung task bug triggered when changing cmdsn_depth invoked session reinstatement while an iscsi login was already waiting for session reinstatement to complete.

This can happen when an outstanding se_cmd descriptor is taking a long time to complete, and session reinstatement from iscsi login or cmdsn_depth change occurs concurrently.

To address this bug, explicitly set session_fall_back_to_erl0 = 1 when forcing session reinstatement, so session reinstatement is not attempted if an active session is already being shutdown.

This patch has been tested with two scenarios. The first when iscsi login is blocked waiting for iscsi session reinstatement to complete followed by queue_depth change via configfs, and second when queue_depth change via configfs us blocked followed by a iscsi login driven session reinstatement.

Note this patch depends on commit d36ad77f702 to handle multiple sessions per se_node_acl when changing cmdsn_depth, and for pre v4.5 kernels will need to be included for stable as well.

---
 drivers/target/iscsi/iscsi_target.c          |    1 +
 drivers/target/iscsi/iscsi_target_configfs.c |    1 +
 drivers/target/iscsi/iscsi_target_login.c    |    1 +
 3 files changed, 3 insertions(+)

@@ -4821,6 +4821,7 @@ int iscsit_release_sessions_for_tpg(stru
 			continue;
 		}
 		atomic_set(&sess->session_reinstatement, 1);
+		atomic_set(&sess->session_fall_back_to_erl0, 1);
 		spin_unlock(&sess->conn_lock);
 
 		list_move_tail(&se_sess->sess_list, &free_list);

@@ -1608,6 +1608,7 @@ static int lio_tpg_shutdown_session(stru
 		return 0;
 	}
 	atomic_set(&sess->session_reinstatement, 1);
+	atomic_set(&sess->session_fall_back_to_erl0, 1);
 	spin_unlock(&sess->conn_lock);
 
 	iscsit_stop_time2retain_timer(sess);

@@ -195,6 +195,7 @@ int iscsi_check_for_session_reinstatemen
 			    initiatorname_param->value) &&
 		   (sess_p->sess_ops->SessionType == sessiontype))) {
 			atomic_set(&sess_p->session_reinstatement, 1);
+			atomic_set(&sess_p->session_fall_back_to_erl0, 1);
 			spin_unlock(&sess_p->conn_lock);
 			iscsit_inc_session_usage_count(sess_p);
 			iscsit_stop_time2retain_timer(sess_p);

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/target-convert-acl-change-queue_depth-se_session-reference-usage.patch queue-4.4/target-fix-compare_and_write_callback-handling-for-non-good-status.patch queue-4.4/target-fileio-fix-zero-length-read-and-write-handling.patch queue-4.4/iscsi-target-set-session_fall_back_to_erl0-when-forcing-reinstatement.patch