In 2.5.52 I broke sys_sync() for ext2 in subtle ways.

sys_sync() will set mapping->dirtied_when non-zero against a clean inode.
Later, in (say) __iget(), that inode gets moved over to inode_unused or
inode_in_use.  But because it has non-zero ->dirtied_when,
__mark_inode_dirty() thinks that the inode must still be on sb->s_dirty.

But it isn't.  It's on inode_in_use.  It (and its pages) never get written
out and the data gets thrown away on unmount.

The patch ceases to use ->dirtied_when as an indicator of inode dirtiness.
Not sure why I even did that :(