linux-kernel - RE: Software raid0 will crash the file-system, when each disk is 5TB

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Date:	Thu, 17 May 2007 15:31:07 +1000
From:	Neil Brown <neilb@...e.de>
To:	david@...g.hm, Jeff Zheng <Jeff.Zheng@...ace.com>,
	Michal Piotrowski <michal.k.k.piotrowski@...il.com>,
	Ingo Molnar <mingo@...e.hu>, linux-raid@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: RE: Software raid0 will crash the file-system, when each disk is
 5TB

On Thursday May 17, neilb@...e.de wrote:
> 
> Uhm, I just noticed something.
> 'chunk' is unsigned long, and when it gets shifted up, we might lose
> bits.  That could still happen with the 4*2.75T arrangement, but is
> much more likely in the 2*5.5T arrangement.

Actually, it cannot be a problem with the 4*2.75T arrangement.
  chuck << chunksize_bits

will not exceed the size of the underlying device *in*kilobytes*.
In that case that is 0xAE9EC800 which will git in a 32bit long.
We don't double it to make sectors until after we add
zone->dev_offset, which is "sector_t" and so 64bit arithmetic is used.

So I'm quite certain this bug will cause exactly the problems
experienced!!

> 
> Jeff, can you try this patch?

Don't bother about the other tests I mentioned, just try this one.
Thanks.

NeilBrown

> Signed-off-by: Neil Brown <neilb@...e.de>
> 
> ### Diffstat output
>  ./drivers/md/raid0.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff .prev/drivers/md/raid0.c ./drivers/md/raid0.c
> --- .prev/drivers/md/raid0.c	2007-05-17 10:33:30.000000000 +1000
> +++ ./drivers/md/raid0.c	2007-05-17 15:02:15.000000000 +1000
> @@ -475,7 +475,7 @@ static int raid0_make_request (request_q
>  		x = block >> chunksize_bits;
>  		tmp_dev = zone->dev[sector_div(x, zone->nb_dev)];
>  	}
> -	rsect = (((chunk << chunksize_bits) + zone->dev_offset)<<1)
> +	rsect = ((((sector_t)chunk << chunksize_bits) + zone->dev_offset)<<1)
>  		+ sect_in_chunk;
>   
>  	bio->bi_bdev = tmp_dev->bdev;
-
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