btrfs: zoned: fix write time activation failure for metadata block group

Since commit 13bb483 ("btrfs: zoned: activate metadata block group on
write time"), we activate a metadata block group at the write time. If the
zone capacity is small enough, we can allocate the entire region before the
first write. Then, we hit the btrfs_zoned_bg_is_full() in
btrfs_zone_activate() and the activation fails.

For a data block group, we activate it at the allocation time and we should
check the fullness condition in the caller side. Add, a WARN to check the
fullness condition.

For a metadata block group, we don't need the fullness check because we
activate it at the write time. Instead, activating it once it is written
should be invalid. Catch that with a WARN too.

Fixes: 13bb483 ("btrfs: zoned: activate metadata block group on write time")
CC: stable@vger.kernel.org # 6.6+
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: naota

fs/btrfs/zoned.c

@@ -2169,10 +2169,15 @@ bool btrfs_zone_activate(struct btrfs_block_group *block_group)
 		goto out_unlock;
 	}
 
-	/* No space left */
-	if (btrfs_zoned_bg_is_full(block_group)) {
-		ret = false;
-		goto out_unlock;
+	if (block_group->flags & BTRFS_BLOCK_GROUP_DATA) {
+		/* The caller should check if the block group is full. */
+		if (WARN_ON_ONCE(btrfs_zoned_bg_is_full(block_group))) {
+			ret = false;
+			goto out_unlock;
+		}
+	} else {
+		/* Since it is already written, it should have been active. */
+		WARN_ON_ONCE(block_group->meta_write_pointer != block_group->start);
 	}
 
 	for (i = 0; i < map->num_stripes; i++) {