Patch "ubi: fastmap: Erase outdated anchor PEBs during attach" has been added to the 4.9-stable tree

@@ -1529,6 +1529,46 @@ static void shutdown_work(struct ubi_dev
 }
 
 /**
+ * erase_aeb - erase a PEB given in UBI attach info PEB
+ * @ubi: UBI device description object
+ * @aeb: UBI attach info PEB
+ * @sync: If true, erase synchronously. Otherwise schedule for erasure
+ */
+static int erase_aeb(struct ubi_device *ubi, struct ubi_ainf_peb *aeb, bool sync)
+{
+	struct ubi_wl_entry *e;
+	int err;
+
+	e = kmem_cache_alloc(ubi_wl_entry_slab, GFP_KERNEL);
+	if (!e)
+		return -ENOMEM;
+
+	e->pnum = aeb->pnum;
+	e->ec = aeb->ec;
+	ubi->lookuptbl[e->pnum] = e;
+
+	if (sync) {
+		err = sync_erase(ubi, e, false);
+		if (err)
+			goto out_free;
+
+		wl_tree_add(e, &ubi->free);
+		ubi->free_count++;
+	} else {
+		err = schedule_erase(ubi, e, aeb->vol_id, aeb->lnum, 0, false);
+		if (err)
+			goto out_free;
+	}
+
+	return 0;
+
+out_free:
+	wl_entry_destroy(ubi, e);
+
+	return err;
+}
+
+/**
  * ubi_wl_init - initialize the WL sub-system using attaching information.
  * @ubi: UBI device description object
  * @ai: attaching information

@@ -1566,17 +1606,9 @@ int ubi_wl_init(struct ubi_device *ubi,
 	list_for_each_entry_safe(aeb, tmp, &ai->erase, u.list) {
 		cond_resched();
 
-		e = kmem_cache_alloc(ubi_wl_entry_slab, GFP_KERNEL);
-		if (!e)
-			goto out_free;
-
-		e->pnum = aeb->pnum;
-		e->ec = aeb->ec;
-		ubi->lookuptbl[e->pnum] = e;
-		if (schedule_erase(ubi, e, aeb->vol_id, aeb->lnum, 0, false)) {
-			wl_entry_destroy(ubi, e);
+		err = erase_aeb(ubi, aeb, false);
+		if (err)
 			goto out_free;
-		}
 
 		found_pebs++;
 	}

@@ -1635,6 +1667,8 @@ int ubi_wl_init(struct ubi_device *ubi,
 			ubi_assert(!ubi->lookuptbl[e->pnum]);
 			ubi->lookuptbl[e->pnum] = e;
 		} else {
+			bool sync = false;
+
 			/*
 			 * Usually old Fastmap PEBs are scheduled for erasure
 			 * and we don't have to care about them but if we face

@@ -1644,18 +1678,21 @@ int ubi_wl_init(struct ubi_device *ubi,
 			if (ubi->lookuptbl[aeb->pnum])
 				continue;
 
-			e = kmem_cache_alloc(ubi_wl_entry_slab, GFP_KERNEL);
-			if (!e)
-				goto out_free;
+			/*
+			 * The fastmap update code might not find a free PEB for
+			 * writing the fastmap anchor to and then reuses the
+			 * current fastmap anchor PEB. When this PEB gets erased
+			 * and a power cut happens before it is written again we
+			 * must make sure that the fastmap attach code doesn't
+			 * find any outdated fastmap anchors, hence we erase the
+			 * outdated fastmap anchor PEBs synchronously here.
+			 */
+			if (aeb->vol_id == UBI_FM_SB_VOLUME_ID)
+				sync = true;
 
-			e->pnum = aeb->pnum;
-			e->ec = aeb->ec;
-			ubi_assert(!ubi->lookuptbl[e->pnum]);
-			ubi->lookuptbl[e->pnum] = e;
-			if (schedule_erase(ubi, e, aeb->vol_id, aeb->lnum, 0, false)) {
-				wl_entry_destroy(ubi, e);
+			err = erase_aeb(ubi, aeb, sync);
+			if (err)
 				goto out_free;
-			}
 		}
 
 		found_pebs++;