From: Jesse Larrew <jlarrew@redhat.com>
Date: Thu, 14 May 2009 00:59:39 -0400
Subject: [scsi] Retry mode select in rdac device handler
Message-id: 20090514045648.10947.8280.sendpatchset@squad5-lp1.lab.bos.redhat.com
O-Subject: [PATCH RHEL5.4 1/10 BZ489582] Retry mode select in rdac device handler
Bugzilla: 489582
RH-Acked-by: Mike Christie <mchristi@redhat.com>

RHBZ#:
======
https://bugzilla.redhat.com/show_bug.cgi?id=489582

Description:
===========
This is a bug fix for all archs.

When the mode select sent to the controller fails with the retryable
error, it is better to retry the mode_select from the hardware handler
itself instead of propagating the failure to dm-multipath.

RHEL Version Found:
================
RHEL 5.3

kABI Status:
============
No symbols were harmed.

Brew:
=====
Built on all platforms.
http://brewweb.devel.redhat.com/brew/taskinfo?taskID=1794596

Upstream Status:
================
commit: c85f8cb9254e60cd25a094329c9dc9185c2140e7

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=c85f8cb9254e60cd25a094329c9dc9185c2140e7

Test Status:
============
This patch has been tested by Chandra Seetharaman at IBM
(sekharan@us.ibm.com).

Testing methodology:
- Configure DS4K storage such that there is at least 1 active path and 1
passive path access from the server.
- Start some I/Os, like disk test on any of the multipath devices.
- Bring the switch port connected to the active controller down and up
(at least after 1 minute).
- Failover _may_ fail due to the failure of mode select failing with some
retryable errors. (In RHEL 5.2 this won't happen).

With this patch applied, failover completes properly.

===============================================================

Jesse Larrew
IBM Onsite Partner
978-392-3183
jlarrew@redhat.com

Proposed Patch:
===============
This patch is based on 2.6.18-136.el5.

diff --git a/drivers/scsi/device_handler/scsi_dh_rdac.c b/drivers/scsi/device_handler/scsi_dh_rdac.c
index 7fa7f51..e33302e 100644
--- a/drivers/scsi/device_handler/scsi_dh_rdac.c
+++ b/drivers/scsi/device_handler/scsi_dh_rdac.c
@@ -27,6 +27,7 @@
 #include "../scsi_priv.h"
 
 #define RDAC_NAME "rdac"
+#define RDAC_RETRY_COUNT 3
 
 /*
  * LSI mode page stuff
@@ -480,21 +481,27 @@ static int send_mode_select(struct scsi_device *sdev, struct rdac_dh_data *h)
 {
 	struct request *rq;
 	struct request_queue *q = sdev->request_queue;
-	int err = SCSI_DH_RES_TEMP_UNAVAIL;
+	int err, retry_cnt = RDAC_RETRY_COUNT;
 
+retry:
+	err = SCSI_DH_RES_TEMP_UNAVAIL;
 	rq = rdac_failover_get(sdev, h);
 	if (!rq)
 		goto done;
 
-	sdev_printk(KERN_INFO, sdev, "queueing MODE_SELECT command.\n");
+	sdev_printk(KERN_INFO, sdev, "%s MODE_SELECT command.\n",
+		(retry_cnt == RDAC_RETRY_COUNT) ? "queueing" : "retrying");
 
 	err = blk_execute_rq(q, NULL, rq, 1);
-	if (err != SCSI_DH_OK)
+	blk_put_request(rq);
+	if (err != SCSI_DH_OK) {
 		err = mode_select_handle_sense(sdev, h->sense);
+		if (err == SCSI_DH_RETRY && retry_cnt--)
+			goto retry;
+	}
 	if (err == SCSI_DH_OK)
 		h->state = RDAC_STATE_ACTIVE;
 
-	blk_put_request(rq);
 done:
 	return err;
 }