I just spent some time researching a Bus Error.  Turns out that the huge
page fault handler can return VM_FAULT_SIGBUS for various conditions where
no huge page is available.

Add a note explaining the reasoning in the source.
Signed-off-by: NChristoph Lameter <clameter@sgi.com>
Acked-by: NWilliam Lee Irwin III <wli@holomorphy.com>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>