[PATCH 3.16 010/306] zfcp: close window with unblocked rport during rport gone

[Ben Hutchings]

3.16.40-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Steffen Maier <maier@xxxxxxxxxxxxxxxxxx>

commit 4eeaa4f3f1d6c47b69f70e222297a4df4743363e upstream.

On a successful end of reopen port forced,
zfcp_erp_strategy_followup_success() re-uses the port erp_action
and the subsequent zfcp_erp_action_cleanup() now
sees ZFCP_ERP_SUCCEEDED with
erp_action->action==ZFCP_ERP_ACTION_REOPEN_PORT
instead of ZFCP_ERP_ACTION_REOPEN_PORT_FORCED
but must not perform zfcp_scsi_schedule_rport_register().

We can detect this because the fresh port reopen erp_action
is in its very first step ZFCP_ERP_STEP_UNINITIALIZED.

Otherwise this opens a time window with unblocked rport
(until the followup port reopen recovery would block it again).
If a scsi_cmnd timeout occurs during this time window
fc_timed_out() cannot work as desired and such command
would indeed time out and trigger scsi_eh. This prevents
a clean and timely path failover.
This should not happen if the path issue can be recovered
on FC transport layer such as path issues involving RSCNs.

Also, unnecessary and repeated DID_IMM_RETRY for pending and
undesired new requests occur because internally zfcp still
has its zfcp_port blocked.

As follow-on errors with scsi_eh, it can cause,
in the worst case, permanently lost paths due to one of:
sd <scsidev>: [<scsidisk>] Medium access timeout failure. Offlining disk!
sd <scsidev>: Device offlined - not ready after error recovery

For fix validation and to aid future debugging with other recoveries
we now also trace (un)blocking of rports.

Signed-off-by: Steffen Maier <maier@xxxxxxxxxxxxxxxxxx>
Fixes: 5767620c383a ("[SCSI] zfcp: Do not unblock rport from REOPEN_PORT_FORCED")
Fixes: a2fa0aede07c ("[SCSI] zfcp: Block FC transport rports early on errors")
Fixes: 5f852be9e11d ("[SCSI] zfcp: Fix deadlock between zfcp ERP and SCSI")
Fixes: 338151e06608 ("[SCSI] zfcp: make use of fc_remote_port_delete when target port is unavailable")
Fixes: 3859f6a248cb ("[PATCH] zfcp: add rports to enable scsi_add_device to work again")
Reviewed-by: Benjamin Block <bblock@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Hannes Reinecke <hare@xxxxxxxx>
Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/s390/scsi/zfcp_dbf.h  |  7 ++++++-
 drivers/s390/scsi/zfcp_erp.c  | 12 +++++++++---
 drivers/s390/scsi/zfcp_scsi.c |  8 +++++++-
 3 files changed, 22 insertions(+), 5 deletions(-)

--- a/drivers/s390/scsi/zfcp_dbf.h
+++ b/drivers/s390/scsi/zfcp_dbf.h
@@ -2,7 +2,7 @@
  * zfcp device driver
  * debug feature declarations
  *
- * Copyright IBM Corp. 2008, 2010
+ * Copyright IBM Corp. 2008, 2015
  */
 
 #ifndef ZFCP_DBF_H
@@ -17,6 +17,11 @@
 
 #define ZFCP_DBF_INVALID_LUN	0xFFFFFFFFFFFFFFFFull
 
+enum zfcp_dbf_pseudo_erp_act_type {
+	ZFCP_PSEUDO_ERP_ACTION_RPORT_ADD = 0xff,
+	ZFCP_PSEUDO_ERP_ACTION_RPORT_DEL = 0xfe,
+};
+
 /**
  * struct zfcp_dbf_rec_trigger - trace record for triggered recovery action
  * @ready: number of ready recovery actions
--- a/drivers/s390/scsi/zfcp_erp.c
+++ b/drivers/s390/scsi/zfcp_erp.c
@@ -3,7 +3,7 @@
  *
  * Error Recovery Procedures (ERP).
  *
- * Copyright IBM Corp. 2002, 2010
+ * Copyright IBM Corp. 2002, 2015
  */
 
 #define KMSG_COMPONENT "zfcp"
@@ -1224,8 +1224,14 @@ static void zfcp_erp_action_cleanup(stru
 		break;
 
 	case ZFCP_ERP_ACTION_REOPEN_PORT:
-		if (result == ZFCP_ERP_SUCCEEDED)
-			zfcp_scsi_schedule_rport_register(port);
+		/* This switch case might also happen after a forced reopen
+		 * was successfully done and thus overwritten with a new
+		 * non-forced reopen at `ersfs_2'. In this case, we must not
+		 * do the clean-up of the non-forced version.
+		 */
+		if (act->step != ZFCP_ERP_STEP_UNINITIALIZED)
+			if (result == ZFCP_ERP_SUCCEEDED)
+				zfcp_scsi_schedule_rport_register(port);
 		/* fall through */
 	case ZFCP_ERP_ACTION_REOPEN_PORT_FORCED:
 		put_device(&port->dev);
--- a/drivers/s390/scsi/zfcp_scsi.c
+++ b/drivers/s390/scsi/zfcp_scsi.c
@@ -3,7 +3,7 @@
  *
  * Interface to Linux SCSI midlayer.
  *
- * Copyright IBM Corp. 2002, 2013
+ * Copyright IBM Corp. 2002, 2015
  */
 
 #define KMSG_COMPONENT "zfcp"
@@ -577,6 +577,9 @@ static void zfcp_scsi_rport_register(str
 	ids.port_id = port->d_id;
 	ids.roles = FC_RPORT_ROLE_FCP_TARGET;
 
+	zfcp_dbf_rec_trig("scpaddy", port->adapter, port, NULL,
+			  ZFCP_PSEUDO_ERP_ACTION_RPORT_ADD,
+			  ZFCP_PSEUDO_ERP_ACTION_RPORT_ADD);
 	rport = fc_remote_port_add(port->adapter->scsi_host, 0, &ids);
 	if (!rport) {
 		dev_err(&port->adapter->ccw_device->dev,
@@ -598,6 +601,9 @@ static void zfcp_scsi_rport_block(struct
 	struct fc_rport *rport = port->rport;
 
 	if (rport) {
+		zfcp_dbf_rec_trig("scpdely", port->adapter, port, NULL,
+				  ZFCP_PSEUDO_ERP_ACTION_RPORT_DEL,
+				  ZFCP_PSEUDO_ERP_ACTION_RPORT_DEL);
 		fc_remote_port_delete(rport);
 		port->rport = NULL;
 	}