mm/huge_memory.c: use head to check huge zero page

The page could be a tail page, if this is the case, this BUG_ON will
never be triggered.

Link: http://lkml.kernel.org/r/[email protected]
Fixes: e9b61f19858a ("thp: reintroduce split_huge_page()")

Signed-off-by: Wei Yang <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
1 file changed