dm space map metadata: fix occasional leak of a metadata block on resize

commit 6096d91a upstream.

The metadata space map has a simplified 'bootstrap' mode that is
operational when extending the space maps.  Whilst in this mode it's
possible for some refcount decrement operations to become queued (eg, as
a result of shadowing one of the bitmap indexes).  These decrements were
not being applied when switching out of bootstrap mode.

The effect of this bug was the leaking of a 4k metadata block.  This is
detected by the latest version of thin_check as a non fatal error.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/md/persistent-data/dm-space-map-metadata.c

@@ -204,19 +204,10 @@ static void in(struct sm_metadata *smm)
 	smm->recursion_count++;
 }
 
-static int out(struct sm_metadata *smm)
+static int apply_bops(struct sm_metadata *smm)
 {
 	int r = 0;
 
-	/*
-	 * If we're not recursing then very bad things are happening.
-	 */
-	if (!smm->recursion_count) {
-		DMERR("lost track of recursion depth");
-		return -ENOMEM;
-	}
-
-	if (smm->recursion_count == 1) {
 	while (!brb_empty(&smm->uncommitted)) {
 		struct block_op bop;
 
@@ -230,8 +221,25 @@ static int out(struct sm_metadata *smm)
 		if (r)
 			break;
 	}
+
+	return r;
+}
+
+static int out(struct sm_metadata *smm)
+{
+	int r = 0;
+
+	/*
+	 * If we're not recursing then very bad things are happening.
+	 */
+	if (!smm->recursion_count) {
+		DMERR("lost track of recursion depth");
+		return -ENOMEM;
 	}
 
+	if (smm->recursion_count == 1)
+		apply_bops(smm);
+
 	smm->recursion_count--;
 
 	return r;
@@ -702,6 +710,12 @@ static int sm_metadata_extend(struct dm_space_map *sm, dm_block_t extra_blocks)
 		}
 		old_len = smm->begin;
 
+		r = apply_bops(smm);
+		if (r) {
+			DMERR("%s: apply_bops failed", __func__);
+			goto out;
+		}
+
 		r = sm_ll_commit(&smm->ll);
 		if (r)
 			goto out;
@@ -771,6 +785,12 @@ int dm_sm_metadata_create(struct dm_space_map *sm,
 	if (r)
 		return r;
 
+	r = apply_bops(smm);
+	if (r) {
+		DMERR("%s: apply_bops failed", __func__);
+		return r;
+	}
+
 	return sm_metadata_commit(sm);
 }