1 files changed, 23 insertions, 8 deletions

diff --git a/mm/frontswap.c b/mm/frontswap.c
index 2760b0f..538367e 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -121,8 +121,13 @@ struct frontswap_ops *frontswap_register_ops(struct frontswap_ops *ops)
 	int i;
 
 	for (i = 0; i < MAX_SWAPFILES; i++) {
-		if (test_and_clear_bit(i, need_init))
+		if (test_and_clear_bit(i, need_init)) {
+			struct swap_info_struct *sis = swap_info[i];
+			/* __frontswap_init _should_ have set it! */
+			if (!sis->frontswap_map)
+				return ERR_PTR(-EINVAL);
 			ops->init(i);
+		}
 	}
 	/*
 	 * We MUST have frontswap_ops set _after_ the frontswap_init's
@@ -156,20 +161,30 @@ EXPORT_SYMBOL(frontswap_tmem_exclusive_gets);
 /*
  * Called when a swap device is swapon'd.
  */
-void __frontswap_init(unsigned type)
+void __frontswap_init(unsigned type, unsigned long *map)
 {
 	struct swap_info_struct *sis = swap_info[type];
 
-	if (frontswap_ops) {
-		BUG_ON(sis == NULL);
-		if (sis->frontswap_map == NULL)
-			return;
+	BUG_ON(sis == NULL);
+
+	/*
+	 * p->frontswap is a bitmap that we MUST have to figure out which page
+	 * has gone in frontswap. Without it there is no point of continuing.
+	 */
+	if (WARN_ON(!map))
+		return;
+	/*
+	 * Irregardless of whether the frontswap backend has been loaded
+	 * before this function or it will be later, we _MUST_ have the
+	 * p->frontswap set to something valid to work properly.
+	 */
+	frontswap_map_set(sis, map);
+	if (frontswap_ops)
 		frontswap_ops->init(type);
-	} else {
+	else {
 		BUG_ON(type > MAX_SWAPFILES);
 		set_bit(type, need_init);
 	}
-
 }
 EXPORT_SYMBOL(__frontswap_init);