[PATCH v2 1/3] null_blk: fix opening closed zones at the active zone limit

[Niklas Cassel <cassel@kernel.org>]

When the open zone limit is reached, null_check_open() closes an
implicitly open zone only if the active zone limit is not reached.

Closing an implicitly open zone does not change the number of active
zones, so this check is wrong. For an empty zone, the active zone limit
was already checked by null_check_zone_resources(). For a closed zone,
the check makes writing to, opening or finishing the zone fail with
BLK_STS_ZONE_OPEN_RESOURCE at the active zone limit, whereas ZBC-3
(4.5.3.2.7.2) and NVMe ZNS (2.1.1.4.1) require closing an implicitly
open zone instead.

Remove the check, and update the comment above
null_check_zone_resources() accordingly.

Fixes: dc4d137ee3b7 ("null_blk: add support for max open/active zone limit for zoned devices")
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
 drivers/block/null_blk/zoned.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/block/null_blk/zoned.c b/drivers/block/null_blk/zoned.c
index 7e9b5ffb9e841..ecdc8d68ca2a9 100644
--- a/drivers/block/null_blk/zoned.c
+++ b/drivers/block/null_blk/zoned.c
@@ -311,10 +311,8 @@ static blk_status_t null_check_open(struct nullb_device *dev)
 		return BLK_STS_OK;
 
 	if (dev->nr_zones_imp_open) {
-		if (null_check_active(dev) == BLK_STS_OK) {
-			null_close_imp_open_zone(dev);
-			return BLK_STS_OK;
-		}
+		null_close_imp_open_zone(dev);
+		return BLK_STS_OK;
 	}
 
 	return BLK_STS_ZONE_OPEN_RESOURCE;
@@ -330,8 +328,11 @@ static blk_status_t null_check_open(struct nullb_device *dev)
  *
  * ZBC states that an implicit open zone shall be closed only if there is not
  * room within the open limit. However, with the addition of an active limit,
- * it is not certain that closing an implicit open zone will allow a new zone
- * to be opened, since we might already be at the active limit capacity.
+ * it is not certain that closing an implicit open zone will allow an empty
+ * zone to be opened, since we might already be at the active limit capacity.
+ * Therefore, the active limit is checked first for an empty zone. A closed
+ * zone already holds an active zone resource, so only the open limit has to
+ * be checked for a closed zone.
  */
 static blk_status_t null_check_zone_resources(struct nullb_device *dev,
 					      struct nullb_zone *zone)
-- 
2.56.0