[PATCH v2] scsi: iscsi: Fix multiple iscsi session unbind event sent to userspace

[Wenchao Hao <haowenchao@huawei.com>]

I found an issue that kernel would send ISCSI_KEVENT_UNBIND_SESSION
for multiple times which should be fixed.

This patch introduce target_unbound in iscsi_cls_session to make
sure session would send only one ISCSI_KEVENT_UNBIND_SESSION.

But this would break issue fixed in commit 13e60d3ba287 ("scsi: iscsi:
Report unbind session event when the target has been removed"). The issue
is iscsid died for any reason after it send unbind session to kernel, once
iscsid restart again, it loss kernel's ISCSI_KEVENT_UNBIND_SESSION event.

Now kernel think iscsi_cls_session has already sent an
ISCSI_KEVENT_UNBIND_SESSION event and would not send it any more. Which
would cause userspace unable to logout. Actually the session is in
invalid state(it's target_id is INVALID), iscsid should not sync this
session in it's restart.

So we need to check session's target unbound state during iscsid restart,
if session is in unbound state, do not sync this session and perform
session teardown. It's reasonable because once a session is unbound, we
can not recover it any more(mainly because it's target id is INVALID)

Changes from V1:
- Using target_unbound rather than state to indicate session has been
  unbound

Signed-off-by: Wenchao Hao <haowenchao@huawei.com>
---
 drivers/scsi/scsi_transport_iscsi.c | 21 +++++++++++++++++++++
 include/scsi/scsi_transport_iscsi.h |  1 +
 2 files changed, 22 insertions(+)

diff --git a/drivers/scsi/scsi_transport_iscsi.c b/drivers/scsi/scsi_transport_iscsi.c
index 2c0dd64159b0..43ba31e595b4 100644
--- a/drivers/scsi/scsi_transport_iscsi.c
+++ b/drivers/scsi/scsi_transport_iscsi.c
@@ -1958,6 +1958,14 @@ static void __iscsi_unbind_session(struct work_struct *work)
 
 	ISCSI_DBG_TRANS_SESSION(session, "Unbinding session\n");
 
+	spin_lock_irqsave(&session->lock, flags);
+	if (session->target_unbound) {
+		spin_unlock_irqrestore(&session->lock, flags);
+		return;
+	}
+	session->target_unbound = 1;
+	spin_unlock_irqrestore(&session->lock, flags);
+
 	/* Prevent new scans and make sure scanning is not in progress */
 	mutex_lock(&ihost->mutex);
 	spin_lock_irqsave(&session->lock, flags);
@@ -2058,6 +2066,7 @@ int iscsi_add_session(struct iscsi_cls_session *session, unsigned int target_id)
 		session->target_id = target_id;
 
 	dev_set_name(&session->dev, "session%u", session->sid);
+	session->target_unbound = 0;
 	err = device_add(&session->dev);
 	if (err) {
 		iscsi_cls_session_printk(KERN_ERR, session,
@@ -4319,6 +4328,15 @@ iscsi_session_attr(def_taskmgmt_tmo, ISCSI_PARAM_DEF_TASKMGMT_TMO, 0);
 iscsi_session_attr(discovery_parent_idx, ISCSI_PARAM_DISCOVERY_PARENT_IDX, 0);
 iscsi_session_attr(discovery_parent_type, ISCSI_PARAM_DISCOVERY_PARENT_TYPE, 0);
 
+static ssize_t
+show_priv_session_target_unbound(struct device *dev, struct device_attribute *attr,
+			char *buf)
+{
+	struct iscsi_cls_session *session = iscsi_dev_to_session(dev->parent);
+	return sysfs_emit(buf, "%d\n", session->target_unbound);
+}
+static ISCSI_CLASS_ATTR(priv_sess, target_unbound, S_IRUGO,
+			show_priv_session_target_unbound, NULL);
 static ssize_t
 show_priv_session_state(struct device *dev, struct device_attribute *attr,
 			char *buf)
@@ -4422,6 +4440,7 @@ static struct attribute *iscsi_session_attrs[] = {
 	&dev_attr_priv_sess_recovery_tmo.attr,
 	&dev_attr_priv_sess_state.attr,
 	&dev_attr_priv_sess_creator.attr,
+	&dev_attr_priv_sess_target_unbound.attr,
 	&dev_attr_sess_chap_out_idx.attr,
 	&dev_attr_sess_chap_in_idx.attr,
 	&dev_attr_priv_sess_target_id.attr,
@@ -4534,6 +4553,8 @@ static umode_t iscsi_session_attr_is_visible(struct kobject *kobj,
 		return S_IRUGO | S_IWUSR;
 	else if (attr == &dev_attr_priv_sess_state.attr)
 		return S_IRUGO;
+	else if (attr == &dev_attr_priv_sess_target_unbound.attr)
+		return S_IRUGO;
 	else if (attr == &dev_attr_priv_sess_creator.attr)
 		return S_IRUGO;
 	else if (attr == &dev_attr_priv_sess_target_id.attr)
diff --git a/include/scsi/scsi_transport_iscsi.h b/include/scsi/scsi_transport_iscsi.h
index 9acb8422f680..877632c25e56 100644
--- a/include/scsi/scsi_transport_iscsi.h
+++ b/include/scsi/scsi_transport_iscsi.h
@@ -256,6 +256,7 @@ struct iscsi_cls_session {
 	struct workqueue_struct *workq;
 
 	unsigned int target_id;
+	int target_unbound;   /* make sure unbind session only once */
 	bool ida_used;
 
 	/*
-- 
2.32.0