mm,memory_hotplug: explicitly pass the head to isolate_huge_page

isolate_huge_page() expects we pass the head of hugetlb page to it:

  bool isolate_huge_page(...)
  {
	...
	VM_BUG_ON_PAGE(!PageHead(page), page);
	...
  }

While I really cannot think of any situation where we end up with a
non-head page between hands in do_migrate_range(), let us make sure the
code is as sane as possible by explicitly passing the Head.  Since we
already got the pointer, it does not take us extra effort.

Link: http://lkml.kernel.org/r/20190208090604.975-1-osalvador@suse.de
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Anthony Yznaga <anthony.yznaga@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index eb1a284..ebc8c1e 100644 (file)
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1378,12 +1378,12 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
 
                if (PageHuge(page)) {
                        struct page *head = compound_head(page);
-                       pfn = page_to_pfn(head) + (1<<compound_order(head)) - 1;
                        if (compound_order(head) > PFN_SECTION_SHIFT) {
                                ret = -EBUSY;
                                break;
                        }
-                       isolate_huge_page(page, &source);
+                       pfn = page_to_pfn(head) + (1<<compound_order(head)) - 1;
+                       isolate_huge_page(head, &source);
                        continue;
                } else if (PageTransHuge(page))
                        pfn = page_to_pfn(compound_head(page))