linux-ext4 - Re: Bug In ext4 in kernels > 2.6.39 - Not mounting with arguments/options I specify in fstab on root remount

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Date:	Sat, 22 Oct 2011 05:32:18 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Matt Parnell <mparnell@...il.com>
Cc:	Eric Sandeen <sandeen@...hat.com>, linux-ext4@...r.kernel.org
Subject: Re: Bug In ext4 in kernels > 2.6.39 - Not mounting with
 arguments/options I specify in fstab on root remount

On Sat, Oct 22, 2011 at 02:51:35AM -0500, Matt Parnell wrote:
> That doesn't really help me at all, it's not
> rootflags=data=writeback causing this, it's starting to make me
> think that arch's init may be to blame, although I previously ruled
> it out...

Well, it looks like rootflags=data=writeback is not making it to the
file system.  That's why it's not showing up in /proc/mounts, from you
showed us.  Can you look at the kernel dmesg?

You should see something like this:

[    1.421146] EXT3-fs (vda): error: couldn't mount because of unsupported optional features (240)
[    1.434057] EXT4-fs (vda): couldn't mount as ext2 due to feature incompatibilities
[    1.454631] EXT4-fs (vda): mounted filesystem with writeback data mode. Opts: data=writeback
[    1.455966] VFS: Mounted root (ext4 filesystem) readonly on device 254:0.

The first line is the failure to mount the root file system as ext3.
The 2nd is the failure to mount the file system as ext2, using the
ext4 file system driver.  The last two lines show the options show the
mount as ext4.

What do those two lines look to you.  If you don't see "Opts:
data=writeback", then somehow the rootflags option isn't getting passed
down to the file system.  Then when you try to remount the file system
read/write, the fact that you have "data=writeback" in your /etc/fstab
causes the failure to remount.

If you simply remove that from /etc/fstab, things should work better.
The remount will preserve whatever data=journalling mode was in use
when the root file system was originallymounted as.  If rootflags is
non-functional, then the file system won't be mounted as
data=writeback, but at least the boot sequence will continue without
blowing out.

							- Ted
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