cannot mount ext3 boot partition as r/w since 2.6.30

[Theodore Tso]

On Wed, May 20, 2009 at 02:02:43PM +0200, Giuseppe Sacco wrote:
> I am testing new kernel on a mips machine (64 bits for kernel, 32 bits
> userland) and I found a problem when mounting the root file system. It
> is an ext3 file system that is correctly mounted as read only. While
> booting the system remount the file system as read/write and keep
> starting all daemons.
> 
> Moving from 2.6.26 to 2.6.30 kernel, I get this error while remounting
> the file system read/write:
> EXT3-fs: cannot change data mode on remount
> 
> My /etc/fstab contains this line:
> /dev/sda1 / ext3 rw,errors=continue,data=ordered,relatime 0 1
> 
> According to mount manuale page, "data=ordered" should be the default
> value and should be harmless.
> Removing option "data=ordered" fix the boot process.
> 
> So, this is my question: is this a standard behaviour? is "data=ordered"
> no more a default value? What should people do when upgrading their
> system to newer kernels?

The default mount option is now data=writeback (although this is
configurable via a compile-time CONFIG option).  In general you don't
have to specify the data= mount option when you are remounting the
filesystem read/write.  If you really want to use data=ordered, you
can either toggle the CONFIG option at compile time, or use the
rootflags= boot command-line option to set the mount options to be
used when originally mounting the root filesystem.

Regards,

					- Ted