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Subject: Re: [PATCH 1/8] scsi: Drop struct Scsi_Host->host_lock around
 SHT->queuecommand()
From: James Bottomley <James.Bottomley@suse.de>
To: "Nicholas A. Bellinger" <nab@linux-iscsi.org>
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Date: Thu, 16 Sep 2010 22:46:11 -0400
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On Thu, 2010-09-16 at 15:35 -0700, Nicholas A. Bellinger wrote:
> From: Nicholas Bellinger <nab@linux-iscsi.org>
> 
> This patch converts scsi_dispatch_cmd() to only hold struct Scsi_Host->host_lock
> for scsi_cmd_get_serial(), and drops the lock because the call into
> the LLD with host->hostt->queuecommand().
> 
> Signed-off-by: Nicholas A. Bellinger <nab@linux-iscsi.org>
> ---
>  drivers/scsi/scsi.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
> index ad0ed21..06e5b3a 100644
> --- a/drivers/scsi/scsi.c
> +++ b/drivers/scsi/scsi.c
> @@ -745,6 +745,7 @@ int scsi_dispatch_cmd(struct scsi_cmnd *cmd)
>  	 * TODO: kill serial or move to blk layer
>  	 */
>  	scsi_cmd_get_serial(host, cmd); 
> +	spin_unlock_irqrestore(host->host_lock, flags);

So at least from where I stand, my object is to reduce the number of
times we take and release the lock, which this doesn't do.  As I said
before: we need to figure out the rest, which likely includes an atomic
for the serial number (which is almost unused).  I think the check
against SHOST_DEL is fine unlocked.

James