[PATCH 3/4] Avoid re-enabling I/O after the transport became offline

[Bart Van Assche <bvanassche@acm.org>]

Disallow the SDEV_TRANSPORT_OFFLINE to SDEV_CANCEL transition such
that no I/O is sent to devices for which the transport is offline.
Notes:
- Functions like sd_shutdown() use scsi_execute_req() and hence
  set the REQ_PREEMPT flag. Such requests are passed to the LLD
  queuecommand callback in the SDEV_CANCEL state.
- This patch does not affect Fibre Channel LLD drivers since these
  drivers invoke fc_remote_port_chkready() before submitting a SCSI
  request to the HBA. That prevents a timeout to occur in state
  SDEV_CANCEL if the transport is offline.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: Mike Christie <michaelc@cs.wisc.edu>
Cc: James Bottomley <JBottomley@Parallels.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Tejun Heo <tj@kernel.org>
---
 drivers/scsi/scsi_lib.c   |    1 -
 drivers/scsi/scsi_sysfs.c |    9 ++++++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 124392f..a0fb56b 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2178,7 +2178,6 @@ scsi_device_set_state(struct scsi_device *sdev, enum scsi_device_state state)
 		case SDEV_RUNNING:
 		case SDEV_QUIESCE:
 		case SDEV_OFFLINE:
-		case SDEV_TRANSPORT_OFFLINE:
 		case SDEV_BLOCK:
 			break;
 		default:
diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index 931a7d9..1711617 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -955,7 +955,14 @@ void __scsi_remove_device(struct scsi_device *sdev)
 	struct device *dev = &sdev->sdev_gendev;
 
 	if (sdev->is_visible) {
-		if (scsi_device_set_state(sdev, SDEV_CANCEL) != 0)
+		/*
+		 * The transition from SDEV_TRANSPORT_OFFLINE into
+		 * SDEV_CANCEL is not allowed since this transition would
+		 * reenable I/O. However, if the device state was already
+		 * SDEV_TRANSPORT_OFFLINE, proceed with device removal.
+		 */
+		if (scsi_device_set_state(sdev, SDEV_CANCEL) != 0 &&
+		    sdev->sdev_state != SDEV_TRANSPORT_OFFLINE)
 			return;
 
 		bsg_unregister_queue(sdev->request_queue);
-- 
1.7.10.4