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From: Gleb Natapov <gleb@redhat.com>
To: Kevin Wolf <kwolf@suse.de>
Cc: Marc Bevand <m.bevand@gmail.com>,
	kvm@vger.kernel.org, qemu-devel@nongnu.org
Subject: Re: qcow2 corruption observed, fixed by reverting old change
Date: Sun, 15 Feb 2009 12:57:18 +0200	[thread overview]
Message-ID: <20090215105718.GH25994@redhat.com> (raw)
In-Reply-To: <49955681.9070301@suse.de>

> > I tested kvm-81 and kvm-83 as well (can't test kvm-80 or older because of the
> > qcow2 performance regression caused by the default writethrough caching policy)
> > but it randomly triggers an even worse bug: the moment I shut down a guest by
> > typing "quit" in the monitor, it sometimes overwrite the first 4kB of the disk
> > image with mostly NUL bytes (!) which completely destroys it. I am familiar with
> > the qcow2 format and apparently this 4kB block seems to be an L2 table with most
> > entries set to zero. I have had to restore at least 6 or 7 disk images from
> > backup after occurences of that bug. My intuition tells me this may be the qcow2
> > code trying to allocate a cluster to write a new L2 table, but not noticing the
> > allocation failed (represented by a 0 offset), and writing the L2 table at that
> > 0 offset, overwriting the qcow2 header.
> > 
> > Fortunately this bug is also fixed by running kvm-75 with block-qcow2.c reverted
> > to its kvm-72 version.
> > 
> > Basically qcow2 in kvm-73 or newer is completely unreliable.
> > 
> > -marc
> 
> I think the corruption is a completely unrelated bug. I would suspect it
> was introduced in one of Gleb's patches in December. Adding him to CC.
> 
I am not able to reproduce this. After more then hundred boot linux; generate
disk io; quit loops all I've got is an image with 7 leaked blocks and
couple of filesystem corruptions that were fixed by fsck.

--
			Gleb.

WARNING: multiple messages have this Message-ID
From: Gleb Natapov <gleb@redhat.com>
To: Kevin Wolf <kwolf@suse.de>
Cc: Marc Bevand <m.bevand@gmail.com>,
	qemu-devel@nongnu.org, kvm@vger.kernel.org
Subject: [Qemu-devel] Re: qcow2 corruption observed, fixed by reverting old change
Date: Sun, 15 Feb 2009 12:57:18 +0200	[thread overview]
Message-ID: <20090215105718.GH25994@redhat.com> (raw)
In-Reply-To: <49955681.9070301@suse.de>

> > I tested kvm-81 and kvm-83 as well (can't test kvm-80 or older because of the
> > qcow2 performance regression caused by the default writethrough caching policy)
> > but it randomly triggers an even worse bug: the moment I shut down a guest by
> > typing "quit" in the monitor, it sometimes overwrite the first 4kB of the disk
> > image with mostly NUL bytes (!) which completely destroys it. I am familiar with
> > the qcow2 format and apparently this 4kB block seems to be an L2 table with most
> > entries set to zero. I have had to restore at least 6 or 7 disk images from
> > backup after occurences of that bug. My intuition tells me this may be the qcow2
> > code trying to allocate a cluster to write a new L2 table, but not noticing the
> > allocation failed (represented by a 0 offset), and writing the L2 table at that
> > 0 offset, overwriting the qcow2 header.
> > 
> > Fortunately this bug is also fixed by running kvm-75 with block-qcow2.c reverted
> > to its kvm-72 version.
> > 
> > Basically qcow2 in kvm-73 or newer is completely unreliable.
> > 
> > -marc
> 
> I think the corruption is a completely unrelated bug. I would suspect it
> was introduced in one of Gleb's patches in December. Adding him to CC.
> 
I am not able to reproduce this. After more then hundred boot linux; generate
disk io; quit loops all I've got is an image with 7 leaked blocks and
couple of filesystem corruptions that were fixed by fsck.

--
			Gleb.

  parent reply	other threads:[~2009-02-15 11:00 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-02-11  7:00 Jamie Lokier
2009-02-11  7:00 ` [Qemu-devel] " Jamie Lokier
2009-02-11  9:57 ` Kevin Wolf
2009-02-11 11:27   ` Jamie Lokier
2009-02-11 11:27     ` Jamie Lokier
2009-02-11 11:41   ` Jamie Lokier
2009-02-11 11:41     ` Jamie Lokier
2009-02-11 12:41     ` Kevin Wolf
2009-02-11 12:41       ` Kevin Wolf
2009-02-11 16:48       ` Jamie Lokier
2009-02-11 16:48         ` Jamie Lokier
2009-02-12 22:57         ` Consul
2009-02-12 22:57           ` [Qemu-devel] " Consul
2009-02-12 23:19           ` Consul
2009-02-12 23:19             ` [Qemu-devel] " Consul
2009-02-13  7:50             ` Marc Bevand
2009-02-16 12:44         ` [Qemu-devel] " Kevin Wolf
2009-02-17  0:43           ` Jamie Lokier
2009-02-17  0:43             ` Jamie Lokier
2009-03-06 22:37         ` Filip Navara
2009-03-06 22:37           ` Filip Navara
2009-02-12  5:45       ` Chris Wright
2009-02-12  5:45         ` Chris Wright
2009-02-12 11:08         ` Johannes Schindelin
2009-02-12 11:08           ` Johannes Schindelin
2009-02-13  6:41 ` Marc Bevand
2009-02-13 11:16   ` Kevin Wolf
2009-02-13 11:16     ` [Qemu-devel] " Kevin Wolf
2009-02-13 16:23     ` Jamie Lokier
2009-02-13 16:23       ` Jamie Lokier
2009-02-13 18:43       ` Chris Wright
2009-02-13 18:43         ` Chris Wright
2009-02-14  6:31       ` Marc Bevand
2009-02-14 22:28         ` Dor Laor
2009-02-14 22:28           ` Dor Laor
2009-02-15  2:27           ` Jamie Lokier
2009-02-15  7:56           ` Marc Bevand
2009-02-15  7:56             ` Marc Bevand
2009-02-15  2:37         ` Jamie Lokier
2009-02-15 10:57     ` Gleb Natapov [this message]
2009-02-15 10:57       ` Gleb Natapov
2009-02-15 11:46       ` Marc Bevand
2009-02-15 11:46         ` [Qemu-devel] " Marc Bevand
2009-02-15 11:54         ` Marc Bevand
2009-02-15 11:54           ` [Qemu-devel] " Marc Bevand

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