null_set_zone_cond() calls null_finish_zone() to release the zone
resources held by a zone before setting it read-only or offline.

For an empty or closed zone, null_finish_zone() first runs the zone
resource checks, which can close an unrelated implicitly open zone, or
fail. As the error is ignored, a failure for a closed zone leaks
nr_zones_closed, permanently lowering the effective active zone limit.

Setting a zone read-only or offline requires no zone resources, so
release the zone resources held by the zone directly instead, using a
new helper, null_release_zone_resources().

Fixes: d3a5738849e0 ("null_blk: support read-only and offline zone conditions")
Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
 drivers/block/null_blk/zoned.c | 35 +++++++++++++++++++++++++++++-----
 1 file changed, 30 insertions(+), 5 deletions(-)

diff --git a/drivers/block/null_blk/zoned.c b/drivers/block/null_blk/zoned.c
index ecdc8d68ca2a..015f5d304c7c 100644
--- a/drivers/block/null_blk/zoned.c
+++ b/drivers/block/null_blk/zoned.c
@@ -743,6 +743,33 @@ blk_status_t null_process_zoned_cmd(struct nullb_cmd *cmd, enum req_op op,
 	}
 }
 
+/*
+ * Release the zone resources held by a zone, before changing the condition of
+ * the zone to a condition that does not hold any zone resources.
+ */
+static void null_release_zone_resources(struct nullb_device *dev,
+					struct nullb_zone *zone)
+{
+	if (!dev->need_zone_res_mgmt)
+		return;
+
+	spin_lock(&dev->zone_res_lock);
+	switch (zone->cond) {
+	case BLK_ZONE_COND_IMP_OPEN:
+		dev->nr_zones_imp_open--;
+		break;
+	case BLK_ZONE_COND_EXP_OPEN:
+		dev->nr_zones_exp_open--;
+		break;
+	case BLK_ZONE_COND_CLOSED:
+		dev->nr_zones_closed--;
+		break;
+	default:
+		break;
+	}
+	spin_unlock(&dev->zone_res_lock);
+}
+
 /*
  * Set a zone in the read-only or offline condition.
  */
@@ -759,8 +786,8 @@ static void null_set_zone_cond(struct nullb_device *dev,
 	 * If the read-only condition is requested again to zones already in
 	 * read-only condition, restore back normal empty condition. Do the same
 	 * if the offline condition is requested for offline zones. Otherwise,
-	 * set the specified zone condition to the zones. Finish the zones
-	 * beforehand to free up zone resources.
+	 * set the specified zone condition to the zones. Release the zone
+	 * resources held by the zones beforehand.
 	 */
 	if (zone->cond == cond) {
 		zone->cond = BLK_ZONE_COND_EMPTY;
@@ -768,9 +795,7 @@ static void null_set_zone_cond(struct nullb_device *dev,
 		if (dev->memory_backed)
 			null_handle_discard(dev, zone->start, zone->len);
 	} else {
-		if (zone->cond != BLK_ZONE_COND_READONLY &&
-		    zone->cond != BLK_ZONE_COND_OFFLINE)
-			null_finish_zone(dev, zone);
+		null_release_zone_resources(dev, zone);
 		zone->cond = cond;
 		zone->wp = NULL_ZONE_INVALID_WP;
 	}
-- 
2.56.0