flush_tlb_range() needs ->page_table_lock when ->mmap_sem is not held

All other callers already hold either ->mmap_sem (exclusive) or
->page_table_lock.  And we need it because some page table flushing
instanced do work explicitly with ge tables.

See e.g.  arch/powerpc/mm/tlb_hash32.c, flush_tlb_range() and
flush_range() in there.  The same goes for uml, with a lot more
extensive playing with page tables.

Almost all callers are actually fine - flush_tlb_range() may have no
need to bother playing with page tables, but it can do so safely; again,
this caller is the sole exception - everything else either has exclusive
->mmap_sem on the mm in question, or mm->page_table_lock is held.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/hugetlb.c

@@ -2277,8 +2277,8 @@ void __unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
 			set_page_dirty(page);
 		list_add(&page->lru, &page_list);
 	}
-	spin_unlock(&mm->page_table_lock);
 	flush_tlb_range(vma, start, end);
+	spin_unlock(&mm->page_table_lock);
 	mmu_notifier_invalidate_range_end(mm, start, end);
 	list_for_each_entry_safe(page, tmp, &page_list, lru) {
 		page_remove_rmap(page);