[Devel] [PATCH RHEL7 COMMIT] ms/iscsi-target: Fix potential dead-lock during node acl delete

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-693.21.1.vz7.46.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-693.21.1.vz7.46.2
------>
commit 8d78cb0af827bc1694b4ac512a8fef7680171f7f
Author: Nicholas Bellinger <nab at linux-iscsi.org>
Date:   Mon Apr 2 17:28:24 2018 +0300

    ms/iscsi-target: Fix potential dead-lock during node acl delete
    
    ML: 26a99c19f810b2593410899a5b304b21b47428a6
    
    This patch is a iscsi-target specific bug-fix for a dead-lock
    that can occur during explicit struct se_node_acl->acl_group
    se_session deletion via configfs rmdir(2), when iscsi-target
    time2retain timer is still active.
    
    It changes iscsi-target to obtain se_portal_group->session_lock
    internally using spin_in_locked() to check for the specific
    se_node_acl configfs shutdown rmdir(2) case.
    
    Note this patch is intended for stable, and the subsequent
    v4.5-rc patch converts target_core_tpg.c to use proper
    se_sess->sess_kref reference counting for both se_node_acl
    deletion + se_node_acl->queue_depth se_session restart.
    
    Reported-by:: Sagi Grimberg <sagig at mellanox.com>
    Cc: Christoph Hellwig <hch at lst.de>
    Cc: Hannes Reinecke <hare at suse.de>
    Cc: Andy Grover <agrover at redhat.com>
    Cc: Mike Christie <michaelc at cs.wisc.edu>
    Cc: stable at vger.kernel.org # 3.10+
    Signed-off-by: Nicholas Bellinger <nab at linux-iscsi.org>
    Signed-off-by: Andrei Vagin <avagin at openvz.org>
---
 drivers/target/iscsi/iscsi_target_configfs.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/target/iscsi/iscsi_target_configfs.c b/drivers/target/iscsi/iscsi_target_configfs.c
index 6d754cfe3fc4..f43e9757366d 100644
--- a/drivers/target/iscsi/iscsi_target_configfs.c
+++ b/drivers/target/iscsi/iscsi_target_configfs.c
@@ -2016,7 +2016,8 @@ static void lio_tpg_release_fabric_acl(
 }
 
 /*
- * Called with spin_lock_bh(struct se_portal_group->session_lock) held..
+ * Called with spin_lock_irq(struct se_portal_group->session_lock) held
+ * or not held.
  *
  * Also, this function calls iscsit_inc_session_usage_count() on the
  * struct iscsi_session in question.
@@ -2024,19 +2025,32 @@ static void lio_tpg_release_fabric_acl(
 static int lio_tpg_shutdown_session(struct se_session *se_sess)
 {
 	struct iscsi_session *sess = se_sess->fabric_sess_ptr;
+	struct se_portal_group *se_tpg = se_sess->se_tpg;
+	bool local_lock = false;
+
+	if (!spin_is_locked(&se_tpg->session_lock)) {
+		spin_lock_irq(&se_tpg->session_lock);
+		local_lock = true;
+	}
 
 	spin_lock(&sess->conn_lock);
 	if (atomic_read(&sess->session_fall_back_to_erl0) ||
 	    atomic_read(&sess->session_logout) ||
 	    (sess->time2retain_timer_flags & ISCSI_TF_EXPIRED)) {
 		spin_unlock(&sess->conn_lock);
+		if (local_lock)
+			spin_unlock_irq(&sess->conn_lock);
 		return 0;
 	}
 	atomic_set(&sess->session_reinstatement, 1);
 	spin_unlock(&sess->conn_lock);
 
 	iscsit_stop_time2retain_timer(sess);
+	spin_unlock_irq(&se_tpg->session_lock);
+
 	iscsit_stop_session(sess, 1, 1);
+	if (!local_lock)
+		spin_lock_irq(&se_tpg->session_lock);
 
 	return 1;
 }