btrfs: zoned: fix block group alloc_offset calculation

alloc_offset is offset from the start of a block group and @offset is
actually an address in logical space. Thus, we need to consider
block_group->start when calculating them.

Fixes: 011b41bf ("btrfs: zoned: advance allocation pointer after tree log node")
CC: stable@vger.kernel.org # 5.12+
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/free-space-cache.c

@@ -2647,8 +2647,11 @@ int btrfs_remove_free_space(struct btrfs_block_group *block_group,
 		 * btrfs_pin_extent_for_log_replay() when replaying the log.
 		 * Advance the pointer not to overwrite the tree-log nodes.
 		 */
-		if (block_group->alloc_offset < offset + bytes)
-			block_group->alloc_offset = offset + bytes;
+		if (block_group->start + block_group->alloc_offset <
+		    offset + bytes) {
+			block_group->alloc_offset =
+				offset + bytes - block_group->start;
+		}
 		return 0;
 	}