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

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Date:	Tue, 10 Mar 2009 12:03:58 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Adrian Hunter <adrian.hunter@...ia.com>
Cc:	"Jorge Boncompte [DTI2]" <jorge@...2.net>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Error testing ext3 on brd ramdisk

On Fri, Mar 06, 2009 at 09:47:32AM +0200, Adrian Hunter wrote:
> Nick Piggin wrote:
> >On Mon, Mar 02, 2009 at 06:42:18PM +0100, Jorge Boncompte [DTI2] wrote:
> >>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.
> >
> >Hi Jorge,
> >
> >Well I found and fixed something :) (see other mail) but I don't know
> >whether that applies to you here if you're running with a single CPU
> >and no preemption. But still, it might be worth trying that patch? I'm
> >sorry I'm still unable to reproduce a problem with your script
> >(although you don't describe how you create the filesystem before
> >you remount it).
> >
> >>From your description, it suggests that the corrupted image is being
> >read from /dev/ram0 (becuase the md5sum passes).
> >
> >In your script, can you run fsck.minix on config.bin when you first
> >create it? What if you unmount /dev/ram0 before copying the image?
> >
> >Thanks,
> >Nick
> 
> Thanks for looking at this.
> 
> I applied both patches and still got:

Hi Adrian,

Thanks for testing... it does seem like the same problem as Jorge has
(inconsistent filesystem metadata / block device contents at unmount).

I'll keep working at it...

Thanks,
Nick
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