[PATCH] scsi_scan: fix queue depth initialisation problem

[PATCH] scsi_scan: fix queue depth initialisation problem

[James Bottomley]

From: James Bottomley <JBottomley@Odin.com>
Date: Sun, 26 Apr 2015 11:52:46 -0700
Subject: [PATCH] scsi_scan: fix queue depth initialisation problem

Currently we blindly use the value of cmd_per_lun as the initial setting for
queue_depth.  This fails miserably (hangs the system) if it is zero, which is
the default value for anything uninitialised in the template.  The net result
is that every host template has to set a value for cmd_per_lun.  Instead, use
a default value of 1 if the actual value is unset.  This should pave the way
for removing cmd_per_lun from all the templates and eventually from SCSI
itself.

Signed-off-by: James Bottomley <JBottomley@Odin.com>

diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index 60aae01..681a59a 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -280,7 +280,8 @@ static struct scsi_device *scsi_alloc_sdev(struct scsi_target *starget,
 				    sdev->host->cmd_per_lun, shost->bqt,
 				    shost->hostt->tag_alloc_policy);
 	}
-	scsi_change_queue_depth(sdev, sdev->host->cmd_per_lun);
+	scsi_change_queue_depth(sdev, sdev->host->cmd_per_lun ?
+					sdev->host->cmd_per_lun : 1);
 
 	scsi_sysfs_device_initialize(sdev);
 

Re: [PATCH] scsi_scan: fix queue depth initialisation problem

[Hannes Reinecke]

On 04/28/2015 11:24 PM, James Bottomley wrote:
> From: James Bottomley <JBottomley@Odin.com>
> Date: Sun, 26 Apr 2015 11:52:46 -0700
> Subject: [PATCH] scsi_scan: fix queue depth initialisation problem
> 
> Currently we blindly use the value of cmd_per_lun as the initial setting for
> queue_depth.  This fails miserably (hangs the system) if it is zero, which is
> the default value for anything uninitialised in the template.  The net result
> is that every host template has to set a value for cmd_per_lun.  Instead, use
> a default value of 1 if the actual value is unset.  This should pave the way
> for removing cmd_per_lun from all the templates and eventually from SCSI
> itself.
> 
> Signed-off-by: James Bottomley <JBottomley@Odin.com>
Tested-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		               zSeries & Storage
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
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Re: [PATCH] scsi_scan: fix queue depth initialisation problem

[Christoph Hellwig]

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>