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, 18 insertions, 13 deletions

diff --git a/drivers/mtd/ubi/fastmap-wl.c b/drivers/mtd/ubi/fastmap-wl.c
index c44c8470247e..426820ab9afe 100644
--- a/drivers/mtd/ubi/fastmap-wl.c
+++ b/drivers/mtd/ubi/fastmap-wl.c
@@ -57,18 +57,6 @@ static void return_unused_pool_pebs(struct ubi_device *ubi,
 	}
 }
 
-static int anchor_pebs_available(struct rb_root *root)
-{
-	struct rb_node *p;
-	struct ubi_wl_entry *e;
-
-	ubi_rb_for_each_entry(p, e, root, u.rb)
-		if (e->pnum < UBI_FM_MAX_START)
-			return 1;
-
-	return 0;
-}
-
 /**
  * ubi_wl_get_fm_peb - find a physical erase block with a given maximal number.
  * @ubi: UBI device description object
@@ -277,8 +265,26 @@ static struct ubi_wl_entry *get_peb_for_wl(struct ubi_device *ubi)
 int ubi_ensure_anchor_pebs(struct ubi_device *ubi)
 {
 	struct ubi_work *wrk;
+	struct ubi_wl_entry *anchor;
 
 	spin_lock(&ubi->wl_lock);
+
+	/* Do we already have an anchor? */
+	if (ubi->fm_anchor) {
+		spin_unlock(&ubi->wl_lock);
+		return 0;
+	}
+
+	/* See if we can find an anchor PEB on the list of free PEBs */
+	anchor = ubi_wl_get_fm_peb(ubi, 1);
+	if (anchor) {
+		ubi->fm_anchor = anchor;
+		spin_unlock(&ubi->wl_lock);
+		return 0;
+	}
+
+	/* No luck, trigger wear leveling to produce a new anchor PEB */
+	ubi->fm_do_produce_anchor = 1;
 	if (ubi->wl_scheduled) {
 		spin_unlock(&ubi->wl_lock);
 		return 0;
@@ -294,7 +300,6 @@ int ubi_ensure_anchor_pebs(struct ubi_device *ubi)
 		return -ENOMEM;
 	}
 
-	wrk->anchor = 1;
 	wrk->func = &wear_leveling_worker;
 	__schedule_ubi_work(ubi, wrk);
 	return 0;