mm: prevent double decrease of nr_reserved_highatomic

[karo-tx-linux.git] / mm / page_alloc.c

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 97170131f2ab94d9c9ff6cb42b950dc5160516c7..8cbc38f923aaf5b8cc3ee391907c9668cc57a5c9 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2085,13 +2085,25 @@ static void unreserve_highatomic_pageblock(const struct alloc_context *ac)
                                continue;
 
                        /*
-                        * It should never happen but changes to locking could
-                        * inadvertently allow a per-cpu drain to add pages
-                        * to MIGRATE_HIGHATOMIC while unreserving so be safe
-                        * and watch for underflows.
+                        * In page freeing path, migratetype change is racy so
+                        * we can counter several free pages in a pageblock
+                        * in this loop althoug we changed the pageblock type
+                        * from highatomic to ac->migratetype. So we should
+                        * adjust the count once.
                         */
-                       zone->nr_reserved_highatomic -= min(pageblock_nr_pages,
-                               zone->nr_reserved_highatomic);
+                       if (get_pageblock_migratetype(page) ==
+                                                       MIGRATE_HIGHATOMIC) {
+                               /*
+                                * It should never happen but changes to
+                                * locking could inadvertently allow a per-cpu
+                                * drain to add pages to MIGRATE_HIGHATOMIC
+                                * while unreserving so be safe and watch for
+                                * underflows.
+                                */
+                               zone->nr_reserved_highatomic -= min(
+                                               pageblock_nr_pages,
+                                               zone->nr_reserved_highatomic);
+                       }
 
                        /*
                         * Convert to ac->migratetype and avoid the normal