target: Re-instate sess_wait_list for target_wait_for_sess_cmds

Switch back to pre commit 1c7b13fe list splicing logic for active I/O
shutdown with tcm_qla2xxx + ib_srpt fabrics.

The original commit was done under the incorrect assumption that it's safe to
walk se_sess->sess_cmd_list unprotected in target_wait_for_sess_cmds() after
sess->sess_tearing_down = 1 has been set by target_sess_cmd_list_set_waiting()
during session shutdown.

So instead of adding sess->sess_cmd_lock protection around sess->sess_cmd_list
during target_wait_for_sess_cmds(), switch back to sess->sess_wait_list to
allow wait_for_completion() + TFO->release_cmd() to occur without having to
walk ->sess_cmd_list after the list_splice.

Also add a check to exit if target_sess_cmd_list_set_waiting() has already
been called, and add a WARN_ON to check for any fabric bug where new se_cmds
are added to sess->sess_cmd_list after sess->sess_tearing_down = 1 has already
been set.

Cc: Joern Engel <joern@logfs.org>
Cc: Roland Dreier <roland@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_transport.c

@@ -221,6 +221,7 @@ struct se_session *transport_init_session(void)
 	INIT_LIST_HEAD(&se_sess->sess_list);
 	INIT_LIST_HEAD(&se_sess->sess_acl_list);
 	INIT_LIST_HEAD(&se_sess->sess_cmd_list);
+	INIT_LIST_HEAD(&se_sess->sess_wait_list);
 	spin_lock_init(&se_sess->sess_cmd_lock);
 	kref_init(&se_sess->sess_kref);
 
@@ -2250,11 +2251,14 @@ void target_sess_cmd_list_set_waiting(struct se_session *se_sess)
 	unsigned long flags;
 
 	spin_lock_irqsave(&se_sess->sess_cmd_lock, flags);
-
-	WARN_ON(se_sess->sess_tearing_down);
+	if (se_sess->sess_tearing_down) {
+		spin_unlock_irqrestore(&se_sess->sess_cmd_lock, flags);
+		return;
+	}
 	se_sess->sess_tearing_down = 1;
+	list_splice_init(&se_sess->sess_cmd_list, &se_sess->sess_wait_list);
 
-	list_for_each_entry(se_cmd, &se_sess->sess_cmd_list, se_cmd_list)
+	list_for_each_entry(se_cmd, &se_sess->sess_wait_list, se_cmd_list)
 		se_cmd->cmd_wait_set = 1;
 
 	spin_unlock_irqrestore(&se_sess->sess_cmd_lock, flags);
@@ -2267,9 +2271,10 @@ EXPORT_SYMBOL(target_sess_cmd_list_set_waiting);
 void target_wait_for_sess_cmds(struct se_session *se_sess)
 {
 	struct se_cmd *se_cmd, *tmp_cmd;
+	unsigned long flags;
 
 	list_for_each_entry_safe(se_cmd, tmp_cmd,
-				&se_sess->sess_cmd_list, se_cmd_list) {
+				&se_sess->sess_wait_list, se_cmd_list) {
 		list_del(&se_cmd->se_cmd_list);
 
 		pr_debug("Waiting for se_cmd: %p t_state: %d, fabric state:"
@@ -2283,6 +2288,11 @@ void target_wait_for_sess_cmds(struct se_session *se_sess)
 
 		se_cmd->se_tfo->release_cmd(se_cmd);
 	}
+
+	spin_lock_irqsave(&se_sess->sess_cmd_lock, flags);
+	WARN_ON(!list_empty(&se_sess->sess_cmd_list));
+	spin_unlock_irqrestore(&se_sess->sess_cmd_lock, flags);
+
 }
 EXPORT_SYMBOL(target_wait_for_sess_cmds);
 

include/target/target_core_base.h

@@ -543,6 +543,7 @@ struct se_session {
 	struct list_head	sess_list;
 	struct list_head	sess_acl_list;
 	struct list_head	sess_cmd_list;
+	struct list_head	sess_wait_list;
 	spinlock_t		sess_cmd_lock;
 	struct kref		sess_kref;
 };