ubi: Fix producing anchor PEBs

When a new fastmap is about to be written UBI must make sure it has a
free block for a fastmap anchor available. For this ubi_update_fastmap()
calls ubi_ensure_anchor_pebs(). This stopped working with 2e8f08deabbc
("ubi: Fix races around ubi_refill_pools()"), with this commit the wear
leveling code is blocked and can no longer produce free PEBs. UBI then
more often than not falls back to write the new fastmap anchor to the
same block it was already on which means the same erase block gets
erased during each fastmap write and wears out quite fast.

As the locking prevents us from producing the anchor PEB when we
actually need it, this patch changes the strategy for creating the
anchor PEB. We no longer create it on demand right before we want to
write a fastmap, but instead we create an anchor PEB right after we have
written a fastmap. This gives us enough time to produce a new anchor PEB
before it is needed. To make sure we have an anchor PEB for the very
first fastmap write we call ubi_ensure_anchor_pebs() during
initialisation as well.

Fixes: 2e8f08deabbc ("ubi: Fix races around ubi_refill_pools()")
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Richard Weinberger <richard@nod.at>

1 files changed, 14 insertions, 18 deletions

diff --git a/drivers/mtd/ubi/wl.c b/drivers/mtd/ubi/wl.c
index 3fcdefe2714d..5d77a38dba54 100644
--- a/drivers/mtd/ubi/wl.c
+++ b/drivers/mtd/ubi/wl.c
@@ -339,13 +339,6 @@ static struct ubi_wl_entry *find_wl_entry(struct ubi_device *ubi,
 		}
 	}
 
-	/* If no fastmap has been written and this WL entry can be used
-	 * as anchor PEB, hold it back and return the second best WL entry
-	 * such that fastmap can use the anchor PEB later. */
-	if (prev_e && !ubi->fm_disabled &&
-	    !ubi->fm && e->pnum < UBI_FM_MAX_START)
-		return prev_e;
-
 	return e;
 }
 
@@ -656,9 +649,6 @@ static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
 {
 	int err, scrubbing = 0, torture = 0, protect = 0, erroneous = 0;
 	int erase = 0, keep = 0, vol_id = -1, lnum = -1;
-#ifdef CONFIG_MTD_UBI_FASTMAP
-	int anchor = wrk->anchor;
-#endif
 	struct ubi_wl_entry *e1, *e2;
 	struct ubi_vid_io_buf *vidb;
 	struct ubi_vid_hdr *vid_hdr;
@@ -698,11 +688,7 @@ static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
 	}
 
 #ifdef CONFIG_MTD_UBI_FASTMAP
-	/* Check whether we need to produce an anchor PEB */
-	if (!anchor)
-		anchor = !anchor_pebs_available(&ubi->free);
-
-	if (anchor) {
+	if (ubi->fm_do_produce_anchor) {
 		e1 = find_anchor_wl_entry(&ubi->used);
 		if (!e1)
 			goto out_cancel;
@@ -719,6 +705,7 @@ static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
 		self_check_in_wl_tree(ubi, e1, &ubi->used);
 		rb_erase(&e1->u.rb, &ubi->used);
 		dbg_wl("anchor-move PEB %d to PEB %d", e1->pnum, e2->pnum);
+		ubi->fm_do_produce_anchor = 0;
 	} else if (!ubi->scrub.rb_node) {
 #else
 	if (!ubi->scrub.rb_node) {
@@ -1051,7 +1038,6 @@ static int ensure_wear_leveling(struct ubi_device *ubi, int nested)
 		goto out_cancel;
 	}
 
-	wrk->anchor = 0;
 	wrk->func = &wear_leveling_worker;
 	if (nested)
 		__schedule_ubi_work(ubi, wrk);
@@ -1093,8 +1079,15 @@ static int __erase_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk)
 	err = sync_erase(ubi, e, wl_wrk->torture);
 	if (!err) {
 		spin_lock(&ubi->wl_lock);
-		wl_tree_add(e, &ubi->free);
-		ubi->free_count++;
+
+		if (!ubi->fm_anchor && e->pnum < UBI_FM_MAX_START) {
+			ubi->fm_anchor = e;
+			ubi->fm_do_produce_anchor = 0;
+		} else {
+			wl_tree_add(e, &ubi->free);
+			ubi->free_count++;
+		}
+
 		spin_unlock(&ubi->wl_lock);
 
 		/*
@@ -1882,6 +1875,9 @@ int ubi_wl_init(struct ubi_device *ubi, struct ubi_attach_info *ai)
 	if (err)
 		goto out_free;
 
+#ifdef CONFIG_MTD_UBI_FASTMAP
+	ubi_ensure_anchor_pebs(ubi);
+#endif
 	return 0;
 
 out_free: