linux-kernel - Re: dm stripe: Fix bounds

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Date:	Thu, 12 Oct 2006 00:01:21 -0400
From:	Phillip Susi <psusi@....rr.com>
To:	Alasdair G Kergon <agk@...hat.com>, Andrew Morton <akpm@...l.org>,
	linux-kernel@...r.kernel.org
Subject: Re: dm stripe: Fix bounds

This patch broke my system.  I am booting from a hardware fakeraid 
consisting of a raid-0 between two WD 36 gig 10,000 rpm raptors on a VIA 
sata raid controller.  The dmraid utility previously would correctly 
configure dm to access the device ( though I did see some of the IO 
errors you mention in my logs ) and now dmraid fails to configure the dm 
table because this patch rejects it.  My working dmraid table follows:

via_hfciifae: 0 144607678 striped 2 128 8:0 0 8:16 0

I believe the correct thing to do is to special case the last stripe in 
the volume like such:

0-31    64-67
32-63   68-71

Alasdair G Kergon wrote:
> From: Kevin Corry <kevcorry@...ibm.com>
> 
> The dm-stripe target currently does not enforce that the size of a stripe 
> device be a multiple of the chunk-size. Under certain conditions, this can 
> lead to I/O requests going off the end of an underlying device. This 
> test-case shows one example.
> 
> echo "0 100 linear /dev/hdb1 0" | dmsetup create linear0
> echo "0 100 linear /dev/hdb1 100" | dmsetup create linear1
> echo "0 200 striped 2 32 /dev/mapper/linear0 0 /dev/mapper/linear1 0" | \
>    dmsetup create stripe0
> dd if=/dev/zero of=/dev/mapper/stripe0 bs=1k
> 
> This will produce the output:
> dd: writing '/dev/mapper/stripe0': Input/output error
> 97+0 records in
> 96+0 records out
> 
> And in the kernel log will be:
> attempt to access beyond end of device
> dm-0: rw=0, want=104, limit=100
> 
> The patch below will check that the table size is a multiple of the stripe 
> chunk-size when the table is created, which will prevent the above striped 
> device from being created.
> 
> This should not affect tools like LVM or EVMS, since in all the cases I can 
> think of, striped devices are always created with the sizes being a multiple 
> of the chunk-size.
> 
> The size of a stripe device must be a multiple of its chunk-size.
> 
> Signed-off-by: Kevin Corry <kevcorry@...ibm.com>
> Signed-Off-By: Alasdair G Kergon <agk@...hat.com>
> 
>  dm-stripe.c |    6 ++++++
>  1 file changed, 6 insertions(+)
> 
> Index: linux-2.6.16-rc5/drivers/md/dm-stripe.c
> ===================================================================
> --- linux-2.6.16-rc5.orig/drivers/md/dm-stripe.c	2006-03-14 18:25:38.000000000 +0000
> +++ linux-2.6.16-rc5/drivers/md/dm-stripe.c	2006-03-15 17:56:37.000000000 +0000
> @@ -103,9 +103,15 @@ static int stripe_ctr(struct dm_target *
>  		return -EINVAL;
>  	}
>  
> +	if (((uint32_t)ti->len) & (chunk_size - 1)) {
> +		ti->error = "dm-stripe: Target length not divisible by "
> +		    "chunk size";
> +		return -EINVAL;
> +	}
> +
>  	width = ti->len;
>  	if (sector_div(width, stripes)) {
> -		ti->error = "dm-stripe: Target length not divisable by "
> +		ti->error = "dm-stripe: Target length not divisible by "
>  		    "number of stripes";
>  		return -EINVAL;
>  	}

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