mm: remove pte_lock_deinit()

Pagetable page doesn't touch page->mapping or have any used field that
overlaps with it.  No need to clear mapping in dtor.  In fact, doing so
might mask problems that otherwise would be detected by bad_page().

Link: http://lkml.kernel.org/r/20181128235525.58780-1-yuzhao@google.com
Signed-off-by: Yu Zhao <yuzhao@google.com>
Reviewed-by: Matthew Wilcox <willy@infradead.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Pavel Tatashin <pasha.tatashin@oracle.com>
Cc: Souptick Joarder <jrdr.linux@gmail.com>
Cc: Logan Gunthorpe <logang@deltatee.com>
Cc: Keith Busch <keith.busch@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mm.h

@@ -1954,13 +1954,6 @@ static inline bool ptlock_init(struct page *page)
 	return true;
 }
 
-/* Reset page->mapping so free_pages_check won't complain. */
-static inline void pte_lock_deinit(struct page *page)
-{
-	page->mapping = NULL;
-	ptlock_free(page);
-}
-
 #else	/* !USE_SPLIT_PTE_PTLOCKS */
 /*
  * We use mm->page_table_lock to guard all pagetable pages of the mm.
@@ -1971,7 +1964,7 @@ static inline spinlock_t *pte_lockptr(struct mm_struct *mm, pmd_t *pmd)
 }
 static inline void ptlock_cache_init(void) {}
 static inline bool ptlock_init(struct page *page) { return true; }
-static inline void pte_lock_deinit(struct page *page) {}
+static inline void ptlock_free(struct page *page) {}
 #endif /* USE_SPLIT_PTE_PTLOCKS */
 
 static inline void pgtable_init(void)
@@ -1991,7 +1984,7 @@ static inline bool pgtable_page_ctor(struct page *page)
 
 static inline void pgtable_page_dtor(struct page *page)
 {
-	pte_lock_deinit(page);
+	ptlock_free(page);
 	__ClearPageTable(page);
 	dec_zone_page_state(page, NR_PAGETABLE);
 }