Using LVM snapshot integration with ext3 I've noted that even if my ext3
filesystem which was
snapshotted was in a clean state at snapshot time (no needs_recovery flag
set) when that filesystem is mounted read-only (via mounting the LVM
snapshot) it appears to still try to modify the filesystem during the mount
procedure as I get back some "Bad lvm_map in ll_rw_blk" messages from LVM.

In all, I gather nothing is truely changed, but it does generate some
debugging noise from the kernel/LVM.  Looking at the code it looks like
this could be related to an iput() of the journal or such possibly, as the
code shows that the journal is the first thing addressed and has many
checks regarding it.