linux-kernel - [PATCH 3.12 099/142] iscsi-target: Fix potential dead-lock during node acl delete

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Message-Id: <31de1ca845b45d4ff902304f35ca704fd51438dd.1456308281.git.jslaby@suse.cz>
Date:	Wed, 24 Feb 2016 11:04:54 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Nicholas Bellinger <nab@...ux-iscsi.org>,
	Christoph Hellwig <hch@....de>, Hannes Reinecke <hare@...e.de>,
	Andy Grover <agrover@...hat.com>,
	Mike Christie <michaelc@...wisc.edu>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 099/142] iscsi-target: Fix potential dead-lock during node acl delete

From: Nicholas Bellinger <nab@...ux-iscsi.org>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 26a99c19f810b2593410899a5b304b21b47428a6 upstream.

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@...lanox.com>
Cc: Christoph Hellwig <hch@....de>
Cc: Hannes Reinecke <hare@...e.de>
Cc: Andy Grover <agrover@...hat.com>
Cc: Mike Christie <michaelc@...wisc.edu>
Signed-off-by: Nicholas Bellinger <nab@...ux-iscsi.org>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 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 8a1bd1af414b..dcebe96d2b23 100644
--- a/drivers/target/iscsi/iscsi_target_configfs.c
+++ b/drivers/target/iscsi/iscsi_target_configfs.c
@@ -1863,7 +1863,8 @@ 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.
@@ -1871,19 +1872,32 @@ 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;
 }
-- 
2.7.1