1 files changed, 75 insertions, 5 deletions

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 57fbb7ced69f..e98bb6ab4f7e 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -54,6 +54,7 @@
 #include <linux/mount.h>
 #include <linux/pseudo_fs.h>
 #include <linux/migrate.h>
+#include <linux/wait.h>
 #include <linux/pagemap.h>
 #include <linux/fs.h>
 
@@ -268,6 +269,10 @@ struct zs_pool {
 #ifdef CONFIG_COMPACTION
 	struct inode *inode;
 	struct work_struct free_work;
+	/* A wait queue for when migration races with async_free_zspage() */
+	struct wait_queue_head migration_wait;
+	atomic_long_t isolated_pages;
+	bool destroying;
 #endif
 };
 
@@ -1862,6 +1867,31 @@ static void dec_zspage_isolation(struct zspage *zspage)
 	zspage->isolated--;
 }
 
+static void putback_zspage_deferred(struct zs_pool *pool,
+				    struct size_class *class,
+				    struct zspage *zspage)
+{
+	enum fullness_group fg;
+
+	fg = putback_zspage(class, zspage);
+	if (fg == ZS_EMPTY)
+		schedule_work(&pool->free_work);
+
+}
+
+static inline void zs_pool_dec_isolated(struct zs_pool *pool)
+{
+	VM_BUG_ON(atomic_long_read(&pool->isolated_pages) <= 0);
+	atomic_long_dec(&pool->isolated_pages);
+	/*
+	 * There's no possibility of racing, since wait_for_isolated_drain()
+	 * checks the isolated count under &class->lock after enqueuing
+	 * on migration_wait.
+	 */
+	if (atomic_long_read(&pool->isolated_pages) == 0 && pool->destroying)
+		wake_up_all(&pool->migration_wait);
+}
+
 static void replace_sub_page(struct size_class *class, struct zspage *zspage,
 				struct page *newpage, struct page *oldpage)
 {
@@ -1931,6 +1961,7 @@ static bool zs_page_isolate(struct page *page, isolate_mode_t mode)
 	 */
 	if (!list_empty(&zspage->list) && !is_zspage_isolated(zspage)) {
 		get_zspage_mapping(zspage, &class_idx, &fullness);
+		atomic_long_inc(&pool->isolated_pages);
 		remove_zspage(class, zspage, fullness);
 	}
 
@@ -2030,8 +2061,16 @@ static int zs_page_migrate(struct address_space *mapping, struct page *newpage,
 	 * Page migration is done so let's putback isolated zspage to
 	 * the list if @page is final isolated subpage in the zspage.
 	 */
-	if (!is_zspage_isolated(zspage))
-		putback_zspage(class, zspage);
+	if (!is_zspage_isolated(zspage)) {
+		/*
+		 * We cannot race with zs_destroy_pool() here because we wait
+		 * for isolation to hit zero before we start destroying.
+		 * Also, we ensure that everyone can see pool->destroying before
+		 * we start waiting.
+		 */
+		putback_zspage_deferred(pool, class, zspage);
+		zs_pool_dec_isolated(pool);
+	}
 
 	reset_page(page);
 	put_page(page);
@@ -2077,13 +2116,12 @@ static void zs_page_putback(struct page *page)
 	spin_lock(&class->lock);
 	dec_zspage_isolation(zspage);
 	if (!is_zspage_isolated(zspage)) {
-		fg = putback_zspage(class, zspage);
 		/*
 		 * Due to page_lock, we cannot free zspage immediately
 		 * so let's defer.
 		 */
-		if (fg == ZS_EMPTY)
-			schedule_work(&pool->free_work);
+		putback_zspage_deferred(pool, class, zspage);
+		zs_pool_dec_isolated(pool);
 	}
 	spin_unlock(&class->lock);
 }
@@ -2107,8 +2145,36 @@ static int zs_register_migration(struct zs_pool *pool)
 	return 0;
 }
 
+static bool pool_isolated_are_drained(struct zs_pool *pool)
+{
+	return atomic_long_read(&pool->isolated_pages) == 0;
+}
+
+/* Function for resolving migration */
+static void wait_for_isolated_drain(struct zs_pool *pool)
+{
+
+	/*
+	 * We're in the process of destroying the pool, so there are no
+	 * active allocations. zs_page_isolate() fails for completely free
+	 * zspages, so we need only wait for the zs_pool's isolated
+	 * count to hit zero.
+	 */
+	wait_event(pool->migration_wait,
+		   pool_isolated_are_drained(pool));
+}
+
 static void zs_unregister_migration(struct zs_pool *pool)
 {
+	pool->destroying = true;
+	/*
+	 * We need a memory barrier here to ensure global visibility of
+	 * pool->destroying. Thus pool->isolated pages will either be 0 in which
+	 * case we don't care, or it will be > 0 and pool->destroying will
+	 * ensure that we wake up once isolation hits 0.
+	 */
+	smp_mb();
+	wait_for_isolated_drain(pool); /* This can block */
 	flush_work(&pool->free_work);
 	iput(pool->inode);
 }
@@ -2346,6 +2412,10 @@ struct zs_pool *zs_create_pool(const char *name)
 	if (!pool->name)
 		goto err;
 
+#ifdef CONFIG_COMPACTION
+	init_waitqueue_head(&pool->migration_wait);
+#endif
+
 	if (create_cache(pool))
 		goto err;