clean_blockdev_aliases() is using the wrong thing to work out how many
filesystem blocks should be invalidated.  It invalidates too many, which can
cause live fs metadata buffers to be invalidated when they are pending
writeout.  It's a filesystem-wrecker, although seems very hard to hit.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>