3 files changed, 54 insertions, 93 deletions
diff --git a/mm/mlock.c b/mm/mlock.c
index 79398200e423..74e5a6547c3d 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -64,6 +64,12 @@ void clear_page_mlock(struct page *page)
 	mod_zone_page_state(page_zone(page), NR_MLOCK,
 			    -hpage_nr_pages(page));
 	count_vm_event(UNEVICTABLE_PGCLEARED);
+	/*
+	 * The previous TestClearPageMlocked() corresponds to the smp_mb()
+	 * in __pagevec_lru_add_fn().
+	 *
+	 * See __pagevec_lru_add_fn for more explanation.
+	 */
 	if (!isolate_lru_page(page)) {
 		putback_lru_page(page);
 	} else {
diff --git a/mm/swap.c b/mm/swap.c
index 567a7b96e41d..2d337710218f 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -446,30 +446,6 @@ void lru_cache_add(struct page *page)
 }
 
 /**
- * add_page_to_unevictable_list - add a page to the unevictable list
- * @page:  the page to be added to the unevictable list
- *
- * Add page directly to its zone's unevictable list.  To avoid races with
- * tasks that might be making the page evictable, through eg. munlock,
- * munmap or exit, while it's not on the lru, we want to add the page
- * while it's locked or otherwise "invisible" to other tasks.  This is
- * difficult to do when using the pagevec cache, so bypass that.
- */
-void add_page_to_unevictable_list(struct page *page)
-{
-	struct pglist_data *pgdat = page_pgdat(page);
-	struct lruvec *lruvec;
-
-	spin_lock_irq(&pgdat->lru_lock);
-	lruvec = mem_cgroup_page_lruvec(page, pgdat);
-	ClearPageActive(page);
-	SetPageUnevictable(page);
-	SetPageLRU(page);
-	add_page_to_lru_list(page, lruvec, LRU_UNEVICTABLE);
-	spin_unlock_irq(&pgdat->lru_lock);
-}
-
-/**
  * lru_cache_add_active_or_unevictable
  * @page:  the page to be added to LRU
  * @vma:   vma in which page is mapped for determining reclaimability
@@ -484,13 +460,9 @@ void lru_cache_add_active_or_unevictable(struct page *page,
 {
 	VM_BUG_ON_PAGE(PageLRU(page), page);
 
-	if (likely((vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) != VM_LOCKED)) {
+	if (likely((vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) != VM_LOCKED))
 		SetPageActive(page);
-		lru_cache_add(page);
-		return;
-	}
-
-	if (!TestSetPageMlocked(page)) {
+	else if (!TestSetPageMlocked(page)) {
 		/*
 		 * We use the irq-unsafe __mod_zone_page_stat because this
 		 * counter is not modified from interrupt context, and the pte
@@ -500,7 +472,7 @@ void lru_cache_add_active_or_unevictable(struct page *page,
 				    hpage_nr_pages(page));
 		count_vm_event(UNEVICTABLE_PGMLOCKED);
 	}
-	add_page_to_unevictable_list(page);
+	lru_cache_add(page);
 }
 
 /*
@@ -886,15 +858,55 @@ void lru_add_page_tail(struct page *page, struct page *page_tail,
 static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
 				 void *arg)
 {
-	int file = page_is_file_cache(page);
-	int active = PageActive(page);
-	enum lru_list lru = page_lru(page);
+	enum lru_list lru;
+	int was_unevictable = TestClearPageUnevictable(page);
 
 	VM_BUG_ON_PAGE(PageLRU(page), page);
 
 	SetPageLRU(page);
+	/*
+	 * Page becomes evictable in two ways:
+	 * 1) Within LRU lock [munlock_vma_pages() and __munlock_pagevec()].
+	 * 2) Before acquiring LRU lock to put the page to correct LRU and then
+	 *   a) do PageLRU check with lock [check_move_unevictable_pages]
+	 *   b) do PageLRU check before lock [clear_page_mlock]
+	 *
+	 * (1) & (2a) are ok as LRU lock will serialize them. For (2b), we need
+	 * following strict ordering:
+	 *
+	 * #0: __pagevec_lru_add_fn		#1: clear_page_mlock
+	 *
+	 * SetPageLRU()				TestClearPageMlocked()
+	 * smp_mb() // explicit ordering	// above provides strict
+	 *					// ordering
+	 * PageMlocked()			PageLRU()
+	 *
+	 *
+	 * if '#1' does not observe setting of PG_lru by '#0' and fails
+	 * isolation, the explicit barrier will make sure that page_evictable
+	 * check will put the page in correct LRU. Without smp_mb(), SetPageLRU
+	 * can be reordered after PageMlocked check and can make '#1' to fail
+	 * the isolation of the page whose Mlocked bit is cleared (#0 is also
+	 * looking at the same page) and the evictable page will be stranded
+	 * in an unevictable LRU.
+	 */
+	smp_mb();
+
+	if (page_evictable(page)) {
+		lru = page_lru(page);
+		update_page_reclaim_stat(lruvec, page_is_file_cache(page),
+					 PageActive(page));
+		if (was_unevictable)
+			count_vm_event(UNEVICTABLE_PGRESCUED);
+	} else {
+		lru = LRU_UNEVICTABLE;
+		ClearPageActive(page);
+		SetPageUnevictable(page);
+		if (!was_unevictable)
+			count_vm_event(UNEVICTABLE_PGCULLED);
+	}
+
 	add_page_to_lru_list(page, lruvec, lru);
-	update_page_reclaim_stat(lruvec, file, active);
 	trace_mm_lru_insertion(page, lru);
 }
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 444749669187..bee53495a829 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -769,64 +769,7 @@ int remove_mapping(struct address_space *mapping, struct page *page)
  */
 void putback_lru_page(struct page *page)
 {
-	bool is_unevictable;
-	int was_unevictable = PageUnevictable(page);
-
-	VM_BUG_ON_PAGE(PageLRU(page), page);
-
-redo:
-	ClearPageUnevictable(page);
-
-	if (page_evictable(page)) {
-		/*
-		 * For evictable pages, we can use the cache.
-		 * In event of a race, worst case is we end up with an
-		 * unevictable page on [in]active list.
-		 * We know how to handle that.
-		 */
-		is_unevictable = false;
-		lru_cache_add(page);
-	} else {
-		/*
-		 * Put unevictable pages directly on zone's unevictable
-		 * list.
-		 */
-		is_unevictable = true;
-		add_page_to_unevictable_list(page);
-		/*
-		 * When racing with an mlock or AS_UNEVICTABLE clearing
-		 * (page is unlocked) make sure that if the other thread
-		 * does not observe our setting of PG_lru and fails
-		 * isolation/check_move_unevictable_pages,
-		 * we see PG_mlocked/AS_UNEVICTABLE cleared below and move
-		 * the page back to the evictable list.
-		 *
-		 * The other side is TestClearPageMlocked() or shmem_lock().
-		 */
-		smp_mb();
-	}
-
-	/*
-	 * page's status can change while we move it among lru. If an evictable
-	 * page is on unevictable list, it never be freed. To avoid that,
-	 * check after we added it to the list, again.
-	 */
-	if (is_unevictable && page_evictable(page)) {
-		if (!isolate_lru_page(page)) {
-			put_page(page);
-			goto redo;
-		}
-		/* This means someone else dropped this page from LRU
-		 * So, it will be freed or putback to LRU again. There is
-		 * nothing to do here.
-		 */
-	}
-
-	if (was_unevictable && !is_unevictable)
-		count_vm_event(UNEVICTABLE_PGRESCUED);
-	else if (!was_unevictable && is_unevictable)
-		count_vm_event(UNEVICTABLE_PGCULLED);
-
+	lru_cache_add(page);
 	put_page(page);		/* drop ref from isolate */
 }