[PATCH] scsi: alua: retry RTPG on a different path after failure

* [PATCH] scsi: alua: retry RTPG on a different path after failure
@ 2021-05-14 15:32 mwilck
  2021-05-22  3:07 ` Martin K. Petersen
  2021-05-26  4:07 ` Martin K. Petersen
  0 siblings, 2 replies; 3+ messages in thread
From: mwilck @ 2021-05-14 15:32 UTC (permalink / raw)
  To: Martin K. Petersen, Hannes Reinecke
  Cc: linux-scsi, James Bottomley, emilne, Martin Wilck

From: Martin Wilck <mwilck@suse.com>

If an RTPG fails, we can't infer anything wrt the state of the
ports in the port group, except that we were unable to reach
the one port on which the RTPG had failed. "offline" is just a
secondary port state, which means that we can't infer the state
of any port in the PG from the failure (in fact, even the failed
port might still be in "active/optimized" primary port access
state).

Therefore, when we encounter an RTPG failure, we should retry the
RTPG on a different port. This avoids falsely setting
port states to offline for unreachable ports. To do this ports
on which an RTPG has failed are temporarily set to "disabled" to
avoid repeating the afiled I/O on the same target port. Once the
RTPG has either succeed on one port or failed on all ports of the
PG, the ports are enabled again.

Signed-off-by: Martin Wilck <mwilck@suse.com>
Signed-off-by: Hannes Reinecke <hare@suse.de>
---
 drivers/scsi/device_handler/scsi_dh_alua.c | 70 +++++++++++++++++++++-
 1 file changed, 67 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c b/drivers/scsi/device_handler/scsi_dh_alua.c
index efa8c0381476..03b7f255644f 100644
--- a/drivers/scsi/device_handler/scsi_dh_alua.c
+++ b/drivers/scsi/device_handler/scsi_dh_alua.c
@@ -88,6 +88,7 @@ struct alua_dh_data {
 	struct scsi_device	*sdev;
 	int			init_error;
 	struct mutex		init_mutex;
+	bool			disabled;
 };
 
 struct alua_queue_data {
@@ -569,6 +570,8 @@ static int alua_rtpg(struct scsi_device *sdev, struct alua_port_group *pg)
 			kfree(buff);
 			if (driver_byte(retval) == DRIVER_ERROR)
 				return SCSI_DH_DEV_TEMP_BUSY;
+			if (host_byte(retval) == DID_NO_CONNECT)
+				return SCSI_DH_RES_TEMP_UNAVAIL;
 			return SCSI_DH_IO;
 		}
 
@@ -807,6 +810,51 @@ static unsigned alua_stpg(struct scsi_device *sdev, struct alua_port_group *pg)
 	return SCSI_DH_RETRY;
 }
 
+static bool alua_rtpg_select_sdev(struct alua_port_group *pg)
+{
+	struct alua_dh_data *h;
+	struct scsi_device *sdev = NULL;
+
+	lockdep_assert_held(&pg->lock);
+	if (WARN_ON(!pg->rtpg_sdev))
+		return false;
+
+	/*
+	 * RCU protection isn't necessary for dh_list here
+	 * as we hold pg->lock, but for access to h->pg.
+	 */
+	rcu_read_lock();
+	list_for_each_entry_rcu(h, &pg->dh_list, node) {
+		if (!h->sdev)
+			continue;
+		if (h->sdev == pg->rtpg_sdev) {
+			h->disabled = true;
+			continue;
+		}
+		if (rcu_dereference(h->pg) == pg &&
+		    !h->disabled &&
+		    !scsi_device_get(h->sdev)) {
+			sdev = h->sdev;
+			break;
+		}
+	}
+	rcu_read_unlock();
+
+	if (!sdev) {
+		pr_warn("%s: no device found for rtpg\n",
+			(pg->device_id_len ?
+			 (char *)pg->device_id_str : "(nameless PG)"));
+		return false;
+	}
+
+	sdev_printk(KERN_INFO, sdev, "rtpg retry on different device\n");
+
+	scsi_device_put(pg->rtpg_sdev);
+	pg->rtpg_sdev = sdev;
+
+	return true;
+}
+
 static void alua_rtpg_work(struct work_struct *work)
 {
 	struct alua_port_group *pg =
@@ -815,6 +863,7 @@ static void alua_rtpg_work(struct work_struct *work)
 	LIST_HEAD(qdata_list);
 	int err = SCSI_DH_OK;
 	struct alua_queue_data *qdata, *tmp;
+	struct alua_dh_data *h;
 	unsigned long flags;
 
 	spin_lock_irqsave(&pg->lock, flags);
@@ -848,9 +897,18 @@ static void alua_rtpg_work(struct work_struct *work)
 		}
 		err = alua_rtpg(sdev, pg);
 		spin_lock_irqsave(&pg->lock, flags);
-		if (err == SCSI_DH_RETRY || pg->flags & ALUA_PG_RUN_RTPG) {
+
+		/* If RTPG failed on the current device, try using another */
+		if (err == SCSI_DH_RES_TEMP_UNAVAIL &&
+		    alua_rtpg_select_sdev(pg))
+			err = SCSI_DH_IMM_RETRY;
+
+		if (err == SCSI_DH_RETRY || err == SCSI_DH_IMM_RETRY ||
+		    pg->flags & ALUA_PG_RUN_RTPG) {
 			pg->flags &= ~ALUA_PG_RUNNING;
-			if (!pg->interval && !(pg->flags & ALUA_PG_RUN_RTPG))
+			if (err == SCSI_DH_IMM_RETRY)
+				pg->interval = 0;
+			else if (!pg->interval && !(pg->flags & ALUA_PG_RUN_RTPG))
 				pg->interval = ALUA_RTPG_RETRY_DELAY;
 			pg->flags |= ALUA_PG_RUN_RTPG;
 			spin_unlock_irqrestore(&pg->lock, flags);
@@ -878,6 +936,12 @@ static void alua_rtpg_work(struct work_struct *work)
 	}
 
 	list_splice_init(&pg->rtpg_list, &qdata_list);
+	/*
+	 * We went through an RTPG, for good or bad.
+	 * Re-enable all devices for the next attempt.
+	 */
+	list_for_each_entry(h, &pg->dh_list, node)
+		h->disabled = false;
 	pg->rtpg_sdev = NULL;
 	spin_unlock_irqrestore(&pg->lock, flags);
 
@@ -962,6 +1026,7 @@ static int alua_initialize(struct scsi_device *sdev, struct alua_dh_data *h)
 	int err = SCSI_DH_DEV_UNSUPP, tpgs;
 
 	mutex_lock(&h->init_mutex);
+	h->disabled = false;
 	tpgs = alua_check_tpgs(sdev);
 	if (tpgs != TPGS_MODE_NONE)
 		err = alua_check_vpd(sdev, h, tpgs);
@@ -1080,7 +1145,6 @@ static void alua_check(struct scsi_device *sdev, bool force)
 		return;
 	}
 	rcu_read_unlock();
-
 	alua_rtpg_queue(pg, sdev, NULL, force);
 	kref_put(&pg->kref, release_port_group);
 }
-- 
2.31.1


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