[RFC][PATCH] limit state change to SDEV_BLOCK devices in scsi_internal_device_unblock

[Takahiro Yasui <tyasui@redhat.com>]

Hi,

This is a patch to fix SCSI timeout error recovery issue which
I posted about one week ago.

  [RFC] SCSI timeout error recovery issue
  http://marc.info/?l=linux-scsi&m=124042136915970&w=2

scsi timeout on two or more devices may cause extremely long execution
time for user applications because SDEV_OFFLINE state is changed to
SDEV_RUNNING state during scsi error recovery procedures triggered by
a bus reset or a host reset of LLD, and scsi timeout can happens on
the same devices many times.

This happens because scsi_internal_device_unblock() changes device's state
to SDEV_RUNNING even if a device in other states than SDEV_BLOCK, but
scsi_internal_device_block() is a pair with scsi_internal_device_unblock()
and only devices in SDEV_BLOCK state are needed to be changed. This patch
adds a check of the current device state so that state change and queue
activation is not executed for devices in SDEV_BLOCK state.

This patch is based on the idea that devices in SDEV_OFFLINE state need to
stay in SDEV_OFFLINE because SDEV_OFFLINE state is done by:

 - All recovery procedures, bus reset and host reset, has already failed
   for devices in SDEV_OFFLINE state.
   (There is no (or rare?) chance to be recovered.)

 - A user has changed the device's state to SDEV_OFFLINE intentionally
   by an interface such as sysfs.
   (A user needs to enable devices in SDEV_OFFLINE state before using
    them again.)

I appreciate any comments and suggestions on this patch.

Regards,
---
Takahiro Yasui
Hitachi Computer Products (America), Inc.


Signed-off-by: Takahiro Yasui <tyasui@redhat.com>
---
 drivers/scsi/scsi_lib.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

Index: linux-2.6.29/drivers/scsi/scsi_lib.c
===================================================================
--- linux-2.6.29.orig/drivers/scsi/scsi_lib.c
+++ linux-2.6.29/drivers/scsi/scsi_lib.c
@@ -2633,9 +2633,12 @@ scsi_internal_device_unblock(struct scsi
 	unsigned long flags;
 	
 	/* 
-	 * Try to transition the scsi device to SDEV_RUNNING
-	 * and goose the device queue if successful.  
+	 * Try to transition the scsi device to SDEV_RUNNING if it is
+	 * SDEV_BLOCK and goose the device queue if successful.
 	 */
+	if (sdev->sdev_state != SDEV_BLOCK)
+		return 0;
+
 	err = scsi_device_set_state(sdev, SDEV_RUNNING);
 	if (err) {
 		err = scsi_device_set_state(sdev, SDEV_CREATED);