mm/memory_hotplug: make sure the pfn is aligned to the order when onlining

mm/memory_hotplug: make sure the pfn is aligned to the order when onlining

Commit a9cd410a3d29 ("mm/page_alloc.c: memory hotplug: free pages as
higher order") assumed that any PFN we get via memory resources is aligned
to to MAX_ORDER - 1, I am not convinced that is always true.  Let's play
safe, check the alignment and fallback to single pages.

akpm: warn in this situation so we get to find out if and why this ever
occurs.

[[email protected]: add WARN_ON_ONCE()]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: David Hildenbrand <[email protected]>
Cc: Arun KS <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Pavel Tatashin <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Bjorn Helgaas <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Nadav Amit <[email protected]>
Cc: Wei Yang <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>