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]>

1 files changed, 3 insertions, 0 deletions

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index b5ad646df86b..aa54e15ea830 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -646,6 +646,9 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
 	 */
 	for (pfn = start_pfn; pfn < end_pfn; pfn += 1ul << order) {
 		order = min(MAX_ORDER - 1, get_order(PFN_PHYS(end_pfn - pfn)));
+		/* __free_pages_core() wants pfns to be aligned to the order */
+		if (WARN_ON_ONCE(!IS_ALIGNED(pfn, 1ul << order)))
+			order = 0;
 		(*online_page_callback)(pfn_to_page(pfn), order);
 	}