linux-kernel - Re: Error testing ext3 on brd ramdisk

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Date:	Mon, 02 Mar 2009 18:42:18 +0100
From:	"Jorge Boncompte [DTI2]" <jorge@...2.net>
To:	npiggin@...e.de
CC:	ext-adrian.hunter@...ia.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: Error testing ext3 on brd ramdisk

Nick Piggin escribió:
> On Fri, Feb 27, 2009 at 07:08:46PM +0100, Jorge Boncompte [DTI2] wrote:
>> 	Hi,
>>
>> 	I have added Nick Piggin to the CC: as maintainer of the brd driver.
>>
>> 	After switching an embedded distribution that /etc on a ramdisk 
>> 	based minix filesystem from 2.6.23.17 to 2.6.29-rcX i am too getting errors 
>> ant the filesystem is corrupted. Does not happen always. The visible 
>> effect with text files after reboot is getting the old version of the 
>> file and "\0"'s at the end.
>>
>> 	Did you found a solution?
> 
> What architectures are you using? It's possible that brd is missing
> a cacheflush. I test it pretty heavily on x86 and no problems, so
> this might point to an arch specific problem.
> 
> ---
>  drivers/block/brd.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6/drivers/block/brd.c
> ===================================================================
> --- linux-2.6.orig/drivers/block/brd.c
> +++ linux-2.6/drivers/block/brd.c
> @@ -275,8 +275,10 @@ static int brd_do_bvec(struct brd_device
>  	if (rw == READ) {
>  		copy_from_brd(mem + off, brd, sector, len);
>  		flush_dcache_page(page);
> -	} else
> +	} else {
> +		flush_dcache_page(page);
>  		copy_to_brd(brd, mem + off, sector, len);
> +	}
>  	kunmap_atomic(mem, KM_USER0);
>  
>  out:

	Hi, I am on 32bits x86, 2 x Xeon with HT CPUs, but I have seen the same 
corruption on a KVM/QEMU guest with single emulated CPU.

	With your patch on top of vanilla 2.6.29-rc3+plus some networking 
patches I still get corruption sometimes.

	The script that saves the configuration does...

------------
mount -no remount,ro /dev/ram0
dd if=/dev/ram0 of=config.bin bs=1k count=1000
mount -no remount,rw /dev/ram0
md5sum config.bin
dd if=config.bin of=/dev/hda1
echo $md5sum | dd of=/dev/hda1 bs=1k seek=1100 count=32
------------

on system boot

------------
CHECK MD5SUM
dd if=/dev/hda1 of=/dev/ram0 bs=1k count=1000
fsck.minix -a /dev/ram0
mount -nt minix /dev/ram0 /etc -o rw
------------

	I have never seen a MD5 failure on boot, just sometimes the filesystem 
is corrupted. Kernel config attached.

	Jorge
-- 
==============================================================
Jorge Boncompte - Ingenieria y Gestion de RED
DTI2 - Desarrollo de la Tecnologia de las Comunicaciones
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View attachment "config-kernel" of type "text/plain" (62841 bytes)