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Date: Thu, 25 May 2017 09:13:55 +1000
From: Dave Chinner <david@fromorbit.com>
Subject: Re: [PATCH 3/3] xfs: freeze rw filesystems just prior to reboot
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To: Chris Murphy <lists@colorremedies.com>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>, xfs <linux-xfs@vger.kernel.org>, Eric Sandeen <sandeen@redhat.com>

On Wed, May 24, 2017 at 12:25:10AM -0600, Chris Murphy wrote:
> On Wed, May 24, 2017 at 12:22 AM, Chris Murphy <lists@colorremedies.com> wrote:
> > Here's an example from an updated system that
> > fails to boot due to zero length grub.cfg;
> >
> > -rw-------. 1 root root 59650987 May 23 18:16
> > initramfs-0-rescue-a0269ef67a5f4c1ca97e0817ac1c4a6d.img
> > -rw-------. 1 root root 19764807 May 23 18:16 initramfs-4.11.0-2.fc26.x86_64.img
> > -rw-r--r--. 1 root root   182704 Feb 10 22:58 memtest86+-5.01
> > -rw-------. 1 root root  3548950 May  9 09:42 System.map-4.11.0-2.fc26.x86_64
> > -rw-------. 1 root root        0 May 15 13:46 System.map-4.11.1-300.fc26.x86_64
> > -rwxr-xr-x. 1 root root  7282776 May 23 18:16
> > vmlinuz-0-rescue-a0269ef67a5f4c1ca97e0817ac1c4a6d
> > -rwxr-xr-x. 1 root root  7282776 May  9 09:43 vmlinuz-4.11.0-2.fc26.x86_64
> > -rwxr-xr-x. 1 root root        0 May 15 13:46 vmlinuz-4.11.1-300.fc26.x86_64
> >
> > -rw-rw-r--. 1 root root    0 May 23 18:44 grub.cfg
> 
> FWIW this was mounted with -o ro,norecovery following an update that
> resulted in the problem of hitting the grub prompt instead of a boot
> menu.

Yup, if the files were sync()d then the file size updates are still
in the journal which has not been replayed. This is what we've been
saying is the problem all along and that a post-update freeze will
work around. If won't fix the fact that the updates are not
fail-safe (crash before freeze will still leave the config file
update in this state), but it will avoid the failure in the "update
successful, reboot without unmounting" scenario being used here.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com