mm: page_table_check: use new iteration API

The page_ext_next() function assumes that page extension objects for a
page order allocation always reside in the same memory section, which may
not be true and could lead to crashes.  Use the new page_ext iteration API
instead.

Link: https://lkml.kernel.org/r/ca2d53a020fe1cd65c442627ff6c0c40d591cbd8.1741301089.git.luizcap@redhat.com
Fixes: cf54f310d0d3 ("mm/hugetlb: use __GFP_COMP for gigantic folios")
Signed-off-by: Luiz Capitulino <luizcap@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/page_table_check.c b/mm/page_table_check.c
index c2b3600429a0c435daba9ad46e2dd608b7885e8a..68109ee93841d51bd3b7ef428327a11489770732 100644 (file)
--- a/mm/page_table_check.c
+++ b/mm/page_table_check.c
@@ -62,24 +62,20 @@ static struct page_table_check *get_page_table_check(struct page_ext *page_ext)
  */
 static void page_table_check_clear(unsigned long pfn, unsigned long pgcnt)
 {
+       struct page_ext_iter iter;
        struct page_ext *page_ext;
        struct page *page;
-       unsigned long i;
        bool anon;
 
        if (!pfn_valid(pfn))
                return;
 
        page = pfn_to_page(pfn);
-       page_ext = page_ext_get(page);
-
-       if (!page_ext)
-               return;
-
        BUG_ON(PageSlab(page));
        anon = PageAnon(page);
 
-       for (i = 0; i < pgcnt; i++) {
+       rcu_read_lock();
+       for_each_page_ext(page, pgcnt, page_ext, iter) {
                struct page_table_check *ptc = get_page_table_check(page_ext);
 
                if (anon) {
@@ -89,9 +85,8 @@ static void page_table_check_clear(unsigned long pfn, unsigned long pgcnt)
                        BUG_ON(atomic_read(&ptc->anon_map_count));
                        BUG_ON(atomic_dec_return(&ptc->file_map_count) < 0);
                }
-               page_ext = page_ext_next(page_ext);
        }
-       page_ext_put(page_ext);
+       rcu_read_unlock();
 }
 
 /*
@@ -102,24 +97,20 @@ static void page_table_check_clear(unsigned long pfn, unsigned long pgcnt)
 static void page_table_check_set(unsigned long pfn, unsigned long pgcnt,
                                 bool rw)
 {
+       struct page_ext_iter iter;
        struct page_ext *page_ext;
        struct page *page;
-       unsigned long i;
        bool anon;
 
        if (!pfn_valid(pfn))
                return;
 
        page = pfn_to_page(pfn);
-       page_ext = page_ext_get(page);
-
-       if (!page_ext)
-               return;
-
        BUG_ON(PageSlab(page));
        anon = PageAnon(page);
 
-       for (i = 0; i < pgcnt; i++) {
+       rcu_read_lock();
+       for_each_page_ext(page, pgcnt, page_ext, iter) {
                struct page_table_check *ptc = get_page_table_check(page_ext);
 
                if (anon) {
@@ -129,9 +120,8 @@ static void page_table_check_set(unsigned long pfn, unsigned long pgcnt,
                        BUG_ON(atomic_read(&ptc->anon_map_count));
                        BUG_ON(atomic_inc_return(&ptc->file_map_count) < 0);
                }
-               page_ext = page_ext_next(page_ext);
        }
-       page_ext_put(page_ext);
+       rcu_read_unlock();
 }
 
 /*
@@ -140,24 +130,19 @@ static void page_table_check_set(unsigned long pfn, unsigned long pgcnt,
  */
 void __page_table_check_zero(struct page *page, unsigned int order)
 {
+       struct page_ext_iter iter;
        struct page_ext *page_ext;
-       unsigned long i;
 
        BUG_ON(PageSlab(page));
 
-       page_ext = page_ext_get(page);
-
-       if (!page_ext)
-               return;
-
-       for (i = 0; i < (1ul << order); i++) {
+       rcu_read_lock();
+       for_each_page_ext(page, 1 << order, page_ext, iter) {
                struct page_table_check *ptc = get_page_table_check(page_ext);
 
                BUG_ON(atomic_read(&ptc->anon_map_count));
                BUG_ON(atomic_read(&ptc->file_map_count));
-               page_ext = page_ext_next(page_ext);
        }
-       page_ext_put(page_ext);
+       rcu_read_unlock();
 }
 
 void __page_table_check_pte_clear(struct mm_struct *mm, pte_t pte)