ubi: fastmap: Check wl_pool for free peb before wear leveling

UBI fetches free peb from wl_pool during wear leveling, so UBI should
check wl_pool's empty status before wear leveling. Otherwise, UBI will
miss wear leveling chances when free pebs are run out.

Signed-off-by: Zhihao Cheng <[e-mail]>
Signed-off-by: Richard Weinberger <[e-mail]>

drivers/mtd/ubi/fastmap-wl.c

···
 	return ret;
 }
 
+/**
+ * next_peb_for_wl - returns next PEB to be used internally by the
+ * WL sub-system.
+ *
+ * @ubi: UBI device description object
+ */
+static struct ubi_wl_entry *next_peb_for_wl(struct ubi_device *ubi)
+{
+	struct ubi_fm_pool *pool = &ubi->fm_wl_pool;
+	int pnum;
+
+	if (pool->used == pool->size)
+		return NULL;
+
+	pnum = pool->pebs[pool->used];
+	return ubi->lookuptbl[pnum];
+}
+
+/**
+ * need_wear_leveling - checks whether to trigger a wear leveling work.
+ * UBI fetches free PEB from wl_pool, we check free PEBs from both 'wl_pool'
+ * and 'ubi->free', because free PEB in 'ubi->free' tree maybe moved into
+ * 'wl_pool' by ubi_refill_pools().
+ *
+ * @ubi: UBI device description object
+ */
+static bool need_wear_leveling(struct ubi_device *ubi)
+{
+	int ec;
+	struct ubi_wl_entry *e;
+
+	if (!ubi->used.rb_node)
+		return false;
+
+	e = next_peb_for_wl(ubi);
+	if (!e) {
+		if (!ubi->free.rb_node)
+			return false;
+		e = find_wl_entry(ubi, &ubi->free, WL_FREE_MAX_DIFF);
+		ec = e->ec;
+	} else {
+		ec = e->ec;
+		if (ubi->free.rb_node) {
+			e = find_wl_entry(ubi, &ubi->free, WL_FREE_MAX_DIFF);
+			ec = max(ec, e->ec);
+		}
+	}
+	e = rb_entry(rb_first(&ubi->used), struct ubi_wl_entry, u.rb);
+
+	return ec - e->ec >= UBI_WL_THRESHOLD;
+}
+
 /* get_peb_for_wl - returns a PEB to be used internally by the WL sub-system.
  *
  * @ubi: UBI device description object

drivers/mtd/ubi/wl.c

···
 	ubi_assert(!ubi->move_from && !ubi->move_to);
 	ubi_assert(!ubi->move_to_put);
 
+#ifdef CONFIG_MTD_UBI_FASTMAP
+	if (!next_peb_for_wl(ubi) ||
+#else
 	if (!ubi->free.rb_node ||
+#endif
 	    (!ubi->used.rb_node && !ubi->scrub.rb_node)) {
 		/*
 		 * No free physical eraseblocks? Well, they must be waiting in
···
 static int ensure_wear_leveling(struct ubi_device *ubi, int nested)
 {
 	int err = 0;
-	struct ubi_wl_entry *e1;
-	struct ubi_wl_entry *e2;
 	struct ubi_work *wrk;
 
 	spin_lock(&ubi->wl_lock);
···
 	 * the WL worker has to be scheduled anyway.
 	 */
 	if (!ubi->scrub.rb_node) {
+#ifdef CONFIG_MTD_UBI_FASTMAP
+		if (!need_wear_leveling(ubi))
+			goto out_unlock;
+#else
+		struct ubi_wl_entry *e1;
+		struct ubi_wl_entry *e2;
+
 		if (!ubi->used.rb_node || !ubi->free.rb_node)
 			/* No physical eraseblocks - no deal */
 			goto out_unlock;
···
 
 		if (!(e2->ec - e1->ec >= UBI_WL_THRESHOLD))
 			goto out_unlock;
+#endif
 		dbg_wl("schedule wear-leveling");
 	} else
 		dbg_wl("schedule scrubbing");

drivers/mtd/ubi/wl.h

···
 static void update_fastmap_work_fn(struct work_struct *wrk);
 static struct ubi_wl_entry *find_anchor_wl_entry(struct rb_root *root);
 static struct ubi_wl_entry *get_peb_for_wl(struct ubi_device *ubi);
+static struct ubi_wl_entry *next_peb_for_wl(struct ubi_device *ubi);
+static bool need_wear_leveling(struct ubi_device *ubi);
 static void ubi_fastmap_close(struct ubi_device *ubi);
 static inline void ubi_fastmap_init(struct ubi_device *ubi, int *count)
 {