powerpc: assert_pte_locked() use pte_offset_map_ro_nolock()

In assert_pte_locked(), we just get the ptl and assert if it was already
held, so convert it to using pte_offset_map_ro_nolock().

Link: https://lkml.kernel.org/r/4255[e-mail]
Signed-off-by: Qi Zheng <[e-mail]>
Acked-by: David Hildenbrand <[e-mail]>
Reviewed-by: Muchun Song <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Mike Rapoport (Microsoft) <[e-mail]>
Cc: Peter Xu <[e-mail]>
Cc: Ryan Roberts <[e-mail]>
Cc: Vishal Moola (Oracle) <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

arch/powerpc/mm/pgtable.c

···
 	 */
 	if (pmd_none(*pmd))
 		return;
-	pte = pte_offset_map_nolock(mm, pmd, addr, &ptl);
+	pte = pte_offset_map_ro_nolock(mm, pmd, addr, &ptl);
 	BUG_ON(!pte);
 	assert_spin_locked(ptl);
 	pte_unmap(pte);