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Old 08-26-2011, 05:53 PM
Konrad Rzeszutek Wilk
 
Default Bug#637234: Bug#637234: linux-image-3.0.0-1-686-pae: I/O errors using ext4 under xen

On Thu, Aug 25, 2011 at 07:47:08AM +0100, Ian Campbell wrote:
> Hi Konrad,
>
> Does this look at all familiar? There is some more info in the full bug
> log at http://bugs.debian.org/637234 . In particular, contrary to the
> message below, the user subsequently confirmed that the issue appears to
> be Xen specific (doesn't happen on native or vmware) and that it arose
> between 2.6.39-2-686-pae and 3.0.0-1-686-pae.
>
> Could it be related to edf6ef59ec7e "xen-blkfront: Introduce
> BLKIF_OP_FLUSH_DISKCACHE support"? That looks like the only pertinent
> change between 2.6.39 and 3.0.


It shouldn't - from the look of it:
[ 0.529412] blkfront: xvdc: barrier: enabled

it looks as if the 'feature-barrier' is used. Not 'feature-flush-cache' -
otherwise you would have seen a message about that.

But then.. 3.0 (and 2.6.39) don't do barriers anymore. However the backend
seems to do it. And from my understanding is that the barrier request
is a superset of a flush request so it should work. Put maybe that is
an incorrect assumption.

One way to make sure that is not the case is to disable barriers in the
guest. Meaning in /etc/fstab have something like this:

/dev/xvdc /blah ext4 errors=remount-ro,barrier=0 0 1


The other question is what version of Dom0 are you running? Is it 2.6.32?
2.6.39?



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Old 08-26-2011, 10:58 PM
Gedalya
 
Default Bug#637234: Bug#637234: linux-image-3.0.0-1-686-pae: I/O errors using ext4 under xen

One way to make sure that is not the case is to disable barriers in the
guest. Meaning in /etc/fstab have something like this:

/dev/xvdc /blah ext4 errors=remount-ro,barrier=0 0 1


That seems to fix it. It was remounting as read only either during the
boot process or immediately after, and now it boots up and seems to stay
up. I'll test laster with a DomU that actually has things running.


This also fixes the reboot problem I noted earlier, init 6 now reboots
the DomU rather than destory it.




The other question is what version of Dom0 are you running? Is it 2.6.32?
2.6.39?

squeeze, running linux-image-2.6.32-5-xen-amd64 2.6.32-35





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Old 08-29-2011, 02:08 PM
Konrad Rzeszutek Wilk
 
Default Bug#637234: Bug#637234: linux-image-3.0.0-1-686-pae: I/O errors using ext4 under xen

On Fri, Aug 26, 2011 at 06:58:34PM -0400, Gedalya wrote:
>
> >One way to make sure that is not the case is to disable barriers in the
> >guest. Meaning in /etc/fstab have something like this:
> >
> >/dev/xvdc /blah ext4 errors=remount-ro,barrier=0 0 1
>
> That seems to fix it. It was remounting as read only either during
> the boot process or immediately after, and now it boots up and seems
> to stay up. I'll test laster with a DomU that actually has things
> running.

Yeeey!
>
> This also fixes the reboot problem I noted earlier, init 6 now
> reboots the DomU rather than destory it.
>
> >
> >The other question is what version of Dom0 are you running? Is it 2.6.32?
> >2.6.39?
> squeeze, running linux-image-2.6.32-5-xen-amd64 2.6.32-35

Oh, I think I know _exactly_ what bug that is:

This git commit:
280802657fb95c52bb5a35d43fea60351883b2af "xen/blkback: When writting barriers set the sector number to zero"
has to be reverted. Specifically:

commit 3f963cae3ef35d26fdd899c08797a598c5ca3e9b
Author: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Date: Tue Jul 19 16:44:42 2011 -0700

Revert "xen/blkback: When writting barriers set the sector number to zero..."

This reverts commit 280802657fb95c52bb5a35d43fea60351883b2af. This patch
is reported to cause disk corruption:

From: "Huang2, Wei" <Wei.Huang2@amd.com>

We recently found a disk corruption issue with SLES11 SP1 guest. Basically
the guest disk becomes non-bootable after guest shutdown. This is a SLES
specific issue as we didn’t see on other Linux and Windows VMs. Here
is the configuration:

============

1. Xen: xen-4.1-testing, changeset 23096

2. Dom0: Jeremy’s latest pvops 6d94b75 (June 1)

3. VM: SLES 11 SP1, installed as physical machine with raw disk format

============

Regarding the disk before corruption, “file sles11sp1.img” command
read: “/root/guests/sles11-sp1/sles11sp1.img: x86 boot sector;
partition 1: ID=0x82, starthead 1, startsector 63, 4208967 sectors;
partition 2: ID=0x83, active, starthead 0, startsector 4209030,
16755795 sectors”. After corruption, it became a data file:
““/root/guests/sles11-sp1/sles11sp1.img: data”.


and this one added:

25266338a41470a21e9b3974445be09e0640dda7
xen/blkback: don't fail empty barrier requests

The sector number on empty barrier requests may (will?) be -1, which,
given that it's being treated as unsigned 64-bit quantity, will almost
always exceed the actual (virtual) disk's size.

Inspired by Konrad's "When writting barriers set the sector number to
zero...".




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Old 09-07-2011, 01:51 AM
Ben Hutchings
 
Default Bug#637234: Bug#637234: linux-image-3.0.0-1-686-pae: I/O errors using ext4 under xen

On Mon, 2011-08-29 at 10:08 -0400, Konrad Rzeszutek Wilk wrote:
[...]
> Oh, I think I know _exactly_ what bug that is:
>
> This git commit:
> 280802657fb95c52bb5a35d43fea60351883b2af "xen/blkback: When writting barriers set the sector number to zero"
> has to be reverted. Specifically:
>
> commit 3f963cae3ef35d26fdd899c08797a598c5ca3e9b
> Author: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
> Date: Tue Jul 19 16:44:42 2011 -0700
>
> Revert "xen/blkback: When writting barriers set the sector number to zero..."
[...]
> and this one added:
>
> 25266338a41470a21e9b3974445be09e0640dda7
> xen/blkback: don't fail empty barrier requests
[...]

Which repository are these in?

Ben.
 
Old 09-07-2011, 12:29 PM
Konrad Rzeszutek Wilk
 
Default Bug#637234: Bug#637234: linux-image-3.0.0-1-686-pae: I/O errors using ext4 under xen

On Wed, Sep 07, 2011 at 02:51:04AM +0100, Ben Hutchings wrote:
> On Mon, 2011-08-29 at 10:08 -0400, Konrad Rzeszutek Wilk wrote:
> [...]
> > Oh, I think I know _exactly_ what bug that is:
> >
> > This git commit:
> > 280802657fb95c52bb5a35d43fea60351883b2af "xen/blkback: When writting barriers set the sector number to zero"
> > has to be reverted. Specifically:
> >
> > commit 3f963cae3ef35d26fdd899c08797a598c5ca3e9b
> > Author: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
> > Date: Tue Jul 19 16:44:42 2011 -0700
> >
> > Revert "xen/blkback: When writting barriers set the sector number to zero..."
> [...]
> > and this one added:
> >
> > 25266338a41470a21e9b3974445be09e0640dda7
> > xen/blkback: don't fail empty barrier requests
> [...]
>
> Which repository are these in?

Jeremy's: git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen.git
>
> Ben.
>
>





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