linux-kernel - [PATCH-v2] target: Avoid target_shutdown_sessions loop during queue

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Message-Id: <1496373093-8852-1-git-send-email-nab@linux-iscsi.org>
Date:   Fri,  2 Jun 2017 03:11:33 +0000
From:   "Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:     target-devel <target-devel@...r.kernel.org>
Cc:     linux-scsi <linux-scsi@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Nicholas Bellinger <nab@...ux-iscsi.org>,
        Christoph Hellwig <hch@....de>,
        Mike Christie <mchristi@...hat.com>,
        Hannes Reinecke <hare@...e.com>
Subject: [PATCH-v2] target: Avoid target_shutdown_sessions loop during queue_depth change

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

When target_shutdown_sessions() is invoked to shutdown all active
sessions associated with a se_node_acl when se_node_acl->queue_depth
is changed via core_tpg_set_initiator_node_queue_depth(), it's
possible that new connections reconnect immediately after explicit
shutdown occurs via target_shutdown_sessions().

Which means it's possible for the newly reconnected session with
the proper queue_depth can be shutdown multiple times when
target_shutdown_sessions() loops to drain all active sessions
for all cases.

This was regression was introduced by:

  commit bc6e6bb470eda42f44bcac96c261cff1216577b3
  Author: Christoph Hellwig <hch@....de>
  Date:   Mon May 2 15:45:19 2016 +0200

      target: consolidate and fix session shutdown

To avoid this case, instead change target_shutdown_sessions() to
pass 'do_restart' and avoid the looping drain of sessions when
invoked via core_tpg_set_initiator_node_queue_depth(), but still
loop during normal se_node_acl delete until all associated
sessions have been shutdown.

(v2 - go back to the original version instead of a local list,
 in order to protect list_del_init(&sess->sess_acl_list) from
 transport_deregister_session_configfs.
 Also use safe list walking in target_shutdown_sessions - nab)

Cc: Christoph Hellwig <hch@....de>
Cc: Mike Christie <mchristi@...hat.com>
Cc: Hannes Reinecke <hare@...e.com>
Signed-off-by: Nicholas Bellinger <nab@...ux-iscsi.org>
---
 drivers/target/target_core_tpg.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/target/target_core_tpg.c b/drivers/target/target_core_tpg.c
index 3691373..1b2b60e 100644
--- a/drivers/target/target_core_tpg.c
+++ b/drivers/target/target_core_tpg.c
@@ -336,14 +336,14 @@ struct se_node_acl *core_tpg_add_initiator_node_acl(
 	return acl;
 }
 
-static void target_shutdown_sessions(struct se_node_acl *acl)
+static void target_shutdown_sessions(struct se_node_acl *acl, bool do_restart)
 {
-	struct se_session *sess;
+	struct se_session *sess, *sess_tmp;
 	unsigned long flags;
 
 restart:
 	spin_lock_irqsave(&acl->nacl_sess_lock, flags);
-	list_for_each_entry(sess, &acl->acl_sess_list, sess_acl_list) {
+	list_for_each_entry_safe(sess, sess_tmp, &acl->acl_sess_list, sess_acl_list) {
 		if (sess->sess_tearing_down)
 			continue;
 
@@ -352,7 +352,11 @@ static void target_shutdown_sessions(struct se_node_acl *acl)
 
 		if (acl->se_tpg->se_tpg_tfo->close_session)
 			acl->se_tpg->se_tpg_tfo->close_session(sess);
-		goto restart;
+
+		if (do_restart)
+			goto restart;
+
+		spin_lock_irqsave(&acl->nacl_sess_lock, flags);
 	}
 	spin_unlock_irqrestore(&acl->nacl_sess_lock, flags);
 }
@@ -367,7 +371,7 @@ void core_tpg_del_initiator_node_acl(struct se_node_acl *acl)
 	list_del(&acl->acl_list);
 	mutex_unlock(&tpg->acl_node_mutex);
 
-	target_shutdown_sessions(acl);
+	target_shutdown_sessions(acl, true);
 
 	target_put_nacl(acl);
 	/*
@@ -414,7 +418,7 @@ int core_tpg_set_initiator_node_queue_depth(
 	/*
 	 * Shutdown all pending sessions to force session reinstatement.
 	 */
-	target_shutdown_sessions(acl);
+	target_shutdown_sessions(acl, false);
 
 	pr_debug("Successfully changed queue depth to: %d for Initiator"
 		" Node: %s on %s Target Portal Group: %u\n", acl->queue_depth,
-- 
1.9.1