linux-kernel - Re: [PATCH] sym53c8xx_2: avoid data corruption when disk rejects commands with QUEUE FULL

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Date:	Sun, 08 May 2011 15:29:55 -0500
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
Cc:	Matthew Wilcox <matthew@....cx>, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sym53c8xx_2: avoid data corruption when disk rejects
 commands with QUEUE FULL

On Sun, 2011-05-08 at 21:00 +0200, Mikulas Patocka wrote:
> [ the maintainer is not responding, so I'm sending this to other people ]
> 
> sym53c8xx_2: avoid data corruption when disk rejects commands with QUEUE 
> FULL

Could you describe the corruption, with logs?  The behaviour you list
below should may cause disk errors to the filesystem, but it shouldn't
cause corruption.

> When the controller encounters an error (including QUEUE FULL or BUSY 
> status), it aborts all not yet submitted requests in the function 
> sym_dequeue_from_squeue.

This would be a driver bug: QUEUE_FULL or BUSY should never cause aborts
of outstanding commands.

> This function aborts them with DID_SOFT_ERROR.
> 
> If the disk has a full tag queue, the request that caused the overflow is
> aborted with QUEUE FULL status (and the scsi midlayer properly retries it
> until it is accepted by the disk), but other requests are aborted with
> DID_SOFT_ERROR --- for them, the midlayer does just a few retries and then
> signals the error up to sd.
> 
> The result is that disk returning QUEUE FULL causes request failures.
> 
> The error was reproduced on 53c895 with COMPAQ BD03685A24 disk (rebranded
> ST336607LC) with command queue 48 or 64 tags. The disk has 64 tags, but
> under some access patterns it return QUEUE FULL when there are less than
> 64 pending tags. The SCSI specification allows returning QUEUE FULL
> anytime and it is up to the host to retry.
> 
> Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>
> 
> ---
>  drivers/scsi/sym53c8xx_2/sym_hipd.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> Index: linux-2.6.36-rc5-fast/drivers/scsi/sym53c8xx_2/sym_hipd.c
> ===================================================================
> --- linux-2.6.36-rc5-fast.orig/drivers/scsi/sym53c8xx_2/sym_hipd.c	2010-09-27 10:25:59.000000000 +0200
> +++ linux-2.6.36-rc5-fast/drivers/scsi/sym53c8xx_2/sym_hipd.c	2010-09-27 10:26:27.000000000 +0200
> @@ -3000,7 +3000,11 @@ sym_dequeue_from_squeue(struct sym_hcb *
>  		if ((target == -1 || cp->target == target) &&
>  		    (lun    == -1 || cp->lun    == lun)    &&
>  		    (task   == -1 || cp->tag    == task)) {
> +#ifdef SYM_OPT_HANDLE_DEVICE_QUEUEING
>  			sym_set_cam_status(cp->cmd, DID_SOFT_ERROR);
> +#else
> +			sym_set_cam_status(cp->cmd, DID_REQUEUE);
> +#endif

This isn't a good idea ... that return code causes retries for ever.  I
think the correct fix is just to make the QUEUE_FULL handling in the
driver work.

James


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