linux-kernel - Re: [PATCH 1/1] um: ubd: Fix data corruption

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Message-Id: <20100928150000.f007f43e.akpm@linux-foundation.org>
Date:	Tue, 28 Sep 2010 15:00:00 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Richard Weinberger <richard@....at>
Cc:	linux-kernel@...r.kernel.org, jdike@...toit.com,
	user-mode-linux-devel@...ts.sourceforge.net,
	user-mode-linux-user@...ts.sourceforge.net, janjaap@....nl,
	geert@...ux-m68k.org, jaxboe@...ionio.com,
	martin.petersen@...cle.com, adobriyan@...il.com,
	cdfrey@...rsquare.net
Subject: Re: [PATCH 1/1] um: ubd: Fix data corruption

On Tue, 28 Sep 2010 23:47:36 +0200
Richard Weinberger <richard@....at> wrote:

> Under high load the file system gets corrupted.
> This patch fixes the issue.
> 
> Many thanks to Janjaap Bos <janjaap@....nl>!
> 
> LKML-Reference: <AANLkTi=PTp7YW_eYxtF-H2QSxgei3whWH59wU0C9oCkz () mail ! gmail ! com>
> Signed-off-by: Richard Weinberger <richard@....at>
> ---
>  arch/um/drivers/ubd_kern.c |    7 +++++--
>  1 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
> index 1bcd208..2874b83 100644
> --- a/arch/um/drivers/ubd_kern.c
> +++ b/arch/um/drivers/ubd_kern.c
> @@ -748,9 +748,12 @@ static int ubd_open_dev(struct ubd *ubd_dev)
>  	}
>  	ubd_dev->fd = fd;
>  
> -	if(ubd_dev->cow.file != NULL){
> -		blk_queue_max_hw_sectors(ubd_dev->queue, 8 * sizeof(long));
> +	/* A setting higher than 1 sector currently (>= v2.6.31) generates
> +		data loss, both for raw and cow ubd. */
> +	blk_queue_max_hw_sectors(ubd_dev->queue, 1 * sizeof(long));
> +	blk_queue_max_segments(ubd_dev->queue, 1 * sizeof(long));
>  
> +	if (ubd_dev->cow.file != NULL) {
>  		err = -ENOMEM;
>  		ubd_dev->cow.bitmap = vmalloc(ubd_dev->cow.bitmap_len);
>  		if(ubd_dev->cow.bitmap == NULL){

This is a workaround, I think?  Do we know what the actual bug is?

>From the comment it appears to be a regression?

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