linux-kernel - Re: [patch] scsi: use lock per host instead of per device for shared queue tag host

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Message-ID: <45B78261.8070604@sgi.com>
Date:	Wed, 24 Jan 2007 09:59:29 -0600
From:	Michael Reed <mdr@....com>
To:	Ed Lin <ed.lin@...mise.com>
CC:	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"james.Bottomley" <james.Bottomley@...elEye.com>,
	jeff <jeff@...zik.org>, promise_linux <promise_linux@...mise.com>
Subject: Re: [patch] scsi: use lock per host instead of per device for shared
 queue tag host

How 'bout a comment in scsh_host.h indicating that the pointer will be NULL unless
initialized by the driver?

"Protect shared block queue tag" is unique to stex.  Perhaps have no comment on
the variable declaration in scsi_host.h and explain why you use it in stex.

Mike


Ed Lin wrote:
> The block layer uses lock to protect request queue. Every scsi device
> has a unique request queue, and queue lock is the default lock in struct
> request_queue. This is good for normal cases. But for a  host with
> shared queue tag (e.g. stex controllers), a queue lock per device means
> the shared queue tag is not protected when multiple devices are accessed
> at a same time.  This patch is a simple fix for this situation by introducing
> a host queue lock to protect shared queue tag. Without this patch we will
> see various kernel panics (including the BUG() and kernel errors in
> blk_queue_start_tag and blk_queue_end_tag of ll_rw_blk.c) when accessing
> different devices simultaneously (e.g. copying big file from one device to
> another in smp kernels).
> 
> This is against kernel 2.6.20-rc5.
> 
> Signed-off-by: Ed Lin <ed.lin@...mise.com>
> ---
>  drivers/scsi/scsi_lib.c  |    2 +-
>  drivers/scsi/stex.c      |    2 ++
>  include/scsi/scsi_host.h |    3 +++
>  3 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff -purN a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> --- a/drivers/scsi/scsi_lib.c	2007-01-23 14:40:28.000000000 -0800
> +++ b/drivers/scsi/scsi_lib.c	2007-01-23 14:46:43.000000000 -0800
> @@ -1574,7 +1574,7 @@ struct request_queue *__scsi_alloc_queue
>  {
>  	struct request_queue *q;
>  
> -	q = blk_init_queue(request_fn, NULL);
> +	q = blk_init_queue(request_fn, shost->req_q_lock);
>  	if (!q)
>  		return NULL;
>  
> diff -purN a/drivers/scsi/stex.c b/drivers/scsi/stex.c
> --- a/drivers/scsi/stex.c	2007-01-23 14:40:28.000000000 -0800
> +++ b/drivers/scsi/stex.c	2007-01-23 14:48:59.000000000 -0800
> @@ -1254,6 +1254,8 @@ stex_probe(struct pci_dev *pdev, const s
>  	if (err)
>  		goto out_free_irq;
>  
> +	spin_lock_init(&host->__req_q_lock);
> +	host->req_q_lock = &host->__req_q_lock;
>  	err = scsi_init_shared_tag_map(host, host->can_queue);
>  	if (err) {
>  		printk(KERN_ERR DRV_NAME "(%s): init shared queue failed\n",
> diff -purN a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
> --- a/include/scsi/scsi_host.h	2007-01-23 14:40:29.000000000 -0800
> +++ b/include/scsi/scsi_host.h	2007-01-23 14:57:04.000000000 -0800
> @@ -508,6 +508,9 @@ struct Scsi_Host {
>  	spinlock_t		default_lock;
>  	spinlock_t		*host_lock;
>  
> +	spinlock_t		__req_q_lock;
> +	spinlock_t		*req_q_lock;/* protect shared block queue tag */
> +
>  	struct mutex		scan_mutex;/* serialize scanning activity */
>  
>  	struct list_head	eh_cmd_q;
> 
> 
> 
> -
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