mm: wrap __find_buddy_pfn() with a necessary buddy page validation

Whenever the buddy of a page is found from __find_buddy_pfn(),
page_is_buddy() should be used to check its validity.  Add a helper
function find_buddy_page_pfn() to find the buddy page and do the check
together.

[ziy@nvidia.com: updates per David]
Link: https://lkml.kernel.org/r/20220401230804.1658207-2-zi.yan@sent.com
Link: https://lore.kernel.org/linux-mm/CAHk-=wji_AmYygZMTsPMdJ7XksMt7kOur8oDfDdniBRMjm4VkQ@mail.gmail.com/
Link: https://lkml.kernel.org/r/7236E7CA-B5F1-4C04-AB85-E86FA3E9A54B@nvidia.com
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Zi Yan <ziy@nvidia.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/internal.h b/mm/internal.h
index cf16280ce132187e5652c5d9088bac716f879a27..6293468fd7b7467a5da15aee83b9b49eadb4684c 100644 (file)
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -211,6 +211,67 @@ struct alloc_context {
        bool spread_dirty_pages;
 };
 
+/*
+ * This function returns the order of a free page in the buddy system. In
+ * general, page_zone(page)->lock must be held by the caller to prevent the
+ * page from being allocated in parallel and returning garbage as the order.
+ * If a caller does not hold page_zone(page)->lock, it must guarantee that the
+ * page cannot be allocated or merged in parallel. Alternatively, it must
+ * handle invalid values gracefully, and use buddy_order_unsafe() below.
+ */
+static inline unsigned int buddy_order(struct page *page)
+{
+       /* PageBuddy() must be checked by the caller */
+       return page_private(page);
+}
+
+/*
+ * Like buddy_order(), but for callers who cannot afford to hold the zone lock.
+ * PageBuddy() should be checked first by the caller to minimize race window,
+ * and invalid values must be handled gracefully.
+ *
+ * READ_ONCE is used so that if the caller assigns the result into a local
+ * variable and e.g. tests it for valid range before using, the compiler cannot
+ * decide to remove the variable and inline the page_private(page) multiple
+ * times, potentially observing different values in the tests and the actual
+ * use of the result.
+ */
+#define buddy_order_unsafe(page)       READ_ONCE(page_private(page))
+
+/*
+ * This function checks whether a page is free && is the buddy
+ * we can coalesce a page and its buddy if
+ * (a) the buddy is not in a hole (check before calling!) &&
+ * (b) the buddy is in the buddy system &&
+ * (c) a page and its buddy have the same order &&
+ * (d) a page and its buddy are in the same zone.
+ *
+ * For recording whether a page is in the buddy system, we set PageBuddy.
+ * Setting, clearing, and testing PageBuddy is serialized by zone->lock.
+ *
+ * For recording page's order, we use page_private(page).
+ */
+static inline bool page_is_buddy(struct page *page, struct page *buddy,
+                                unsigned int order)
+{
+       if (!page_is_guard(buddy) && !PageBuddy(buddy))
+               return false;
+
+       if (buddy_order(buddy) != order)
+               return false;
+
+       /*
+        * zone check is done late to avoid uselessly calculating
+        * zone/node ids for pages that could never merge.
+        */
+       if (page_zone_id(page) != page_zone_id(buddy))
+               return false;
+
+       VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy);
+
+       return true;
+}
+
 /*
  * Locate the struct page for both the matching buddy in our
  * pair (buddy1) and the combined O(n+1) page they form (page).
@@ -234,6 +295,35 @@ __find_buddy_pfn(unsigned long page_pfn, unsigned int order)
        return page_pfn ^ (1 << order);
 }
 
+/*
+ * Find the buddy of @page and validate it.
+ * @page: The input page
+ * @pfn: The pfn of the page, it saves a call to page_to_pfn() when the
+ *       function is used in the performance-critical __free_one_page().
+ * @order: The order of the page
+ * @buddy_pfn: The output pointer to the buddy pfn, it also saves a call to
+ *             page_to_pfn().
+ *
+ * The found buddy can be a non PageBuddy, out of @page's zone, or its order is
+ * not the same as @page. The validation is necessary before use it.
+ *
+ * Return: the found buddy page or NULL if not found.
+ */
+static inline struct page *find_buddy_page_pfn(struct page *page,
+                       unsigned long pfn, unsigned int order, unsigned long *buddy_pfn)
+{
+       unsigned long __buddy_pfn = __find_buddy_pfn(pfn, order);
+       struct page *buddy;
+
+       buddy = page + (__buddy_pfn - pfn);
+       if (buddy_pfn)
+               *buddy_pfn = __buddy_pfn;
+
+       if (page_is_buddy(page, buddy, order))
+               return buddy;
+       return NULL;
+}
+
 extern struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
                                unsigned long end_pfn, struct zone *zone);
 
@@ -336,33 +426,6 @@ isolate_migratepages_range(struct compact_control *cc,
 int find_suitable_fallback(struct free_area *area, unsigned int order,
                        int migratetype, bool only_stealable, bool *can_steal);
 
-/*
- * This function returns the order of a free page in the buddy system. In
- * general, page_zone(page)->lock must be held by the caller to prevent the
- * page from being allocated in parallel and returning garbage as the order.
- * If a caller does not hold page_zone(page)->lock, it must guarantee that the
- * page cannot be allocated or merged in parallel. Alternatively, it must
- * handle invalid values gracefully, and use buddy_order_unsafe() below.
- */
-static inline unsigned int buddy_order(struct page *page)
-{
-       /* PageBuddy() must be checked by the caller */
-       return page_private(page);
-}
-
-/*
- * Like buddy_order(), but for callers who cannot afford to hold the zone lock.
- * PageBuddy() should be checked first by the caller to minimize race window,
- * and invalid values must be handled gracefully.
- *
- * READ_ONCE is used so that if the caller assigns the result into a local
- * variable and e.g. tests it for valid range before using, the compiler cannot
- * decide to remove the variable and inline the page_private(page) multiple
- * times, potentially observing different values in the tests and the actual
- * use of the result.
- */
-#define buddy_order_unsafe(page)       READ_ONCE(page_private(page))
-
 /*
  * These three helpers classifies VMAs for virtual memory accounting.
  */

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 26dea6cd3f53aaa47cf3a7c30ecb1e8598eb853e..8de8d7a5c3e37adce929304a7846ff064fa5cfc0 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -867,40 +867,6 @@ static inline void set_buddy_order(struct page *page, unsigned int order)
        __SetPageBuddy(page);
 }
 
-/*
- * This function checks whether a page is free && is the buddy
- * we can coalesce a page and its buddy if
- * (a) the buddy is not in a hole (check before calling!) &&
- * (b) the buddy is in the buddy system &&
- * (c) a page and its buddy have the same order &&
- * (d) a page and its buddy are in the same zone.
- *
- * For recording whether a page is in the buddy system, we set PageBuddy.
- * Setting, clearing, and testing PageBuddy is serialized by zone->lock.
- *
- * For recording page's order, we use page_private(page).
- */
-static inline bool page_is_buddy(struct page *page, struct page *buddy,
-                                                       unsigned int order)
-{
-       if (!page_is_guard(buddy) && !PageBuddy(buddy))
-               return false;
-
-       if (buddy_order(buddy) != order)
-               return false;
-
-       /*
-        * zone check is done late to avoid uselessly calculating
-        * zone/node ids for pages that could never merge.
-        */
-       if (page_zone_id(page) != page_zone_id(buddy))
-               return false;
-
-       VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy);
-
-       return true;
-}
-
 #ifdef CONFIG_COMPACTION
 static inline struct capture_control *task_capc(struct zone *zone)
 {
@@ -1009,18 +975,17 @@ static inline bool
 buddy_merge_likely(unsigned long pfn, unsigned long buddy_pfn,
                   struct page *page, unsigned int order)
 {
-       struct page *higher_page, *higher_buddy;
-       unsigned long combined_pfn;
+       unsigned long higher_page_pfn;
+       struct page *higher_page;
 
        if (order >= MAX_ORDER - 2)
                return false;
 
-       combined_pfn = buddy_pfn & pfn;
-       higher_page = page + (combined_pfn - pfn);
-       buddy_pfn = __find_buddy_pfn(combined_pfn, order + 1);
-       higher_buddy = higher_page + (buddy_pfn - combined_pfn);
+       higher_page_pfn = buddy_pfn & pfn;
+       higher_page = page + (higher_page_pfn - pfn);
 
-       return page_is_buddy(higher_page, higher_buddy, order + 1);
+       return find_buddy_page_pfn(higher_page, higher_page_pfn, order + 1,
+                       NULL) != NULL;
 }
 
 /*
@@ -1074,10 +1039,9 @@ static inline void __free_one_page(struct page *page,
                                                                migratetype);
                        return;
                }
-               buddy_pfn = __find_buddy_pfn(pfn, order);
-               buddy = page + (buddy_pfn - pfn);
 
-               if (!page_is_buddy(page, buddy, order))
+               buddy = find_buddy_page_pfn(page, pfn, order, &buddy_pfn);
+               if (!buddy)
                        goto done_merging;
 
                if (unlikely(order >= pageblock_order)) {

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index f67c4c70f17f66c08626f57b1999462782395eff..ff0ea6308299b20fd4eff311357b6fab14799ff9 100644 (file)
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -70,7 +70,6 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
        unsigned long flags, nr_pages;
        bool isolated_page = false;
        unsigned int order;
-       unsigned long pfn, buddy_pfn;
        struct page *buddy;
 
        zone = page_zone(page);
@@ -89,11 +88,9 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
        if (PageBuddy(page)) {
                order = buddy_order(page);
                if (order >= pageblock_order && order < MAX_ORDER - 1) {
-                       pfn = page_to_pfn(page);
-                       buddy_pfn = __find_buddy_pfn(pfn, order);
-                       buddy = page + (buddy_pfn - pfn);
-
-                       if (!is_migrate_isolate_page(buddy)) {
+                       buddy = find_buddy_page_pfn(page, page_to_pfn(page),
+                                                   order, NULL);
+                       if (buddy && !is_migrate_isolate_page(buddy)) {
                                isolated_page = !!__isolate_free_page(page, order);
                                /*
                                 * Isolating a free page in an isolated pageblock