Btrfs: fix mount failure when qgroup rescan is in progress

If a power failure happens while the qgroup rescan kthread is running,
the next mount operation will always fail. This is because of a recent
regression that makes qgroup_rescan_init() incorrectly return -EINVAL
when we are mounting the filesystem (through btrfs_read_qgroup_config()).
This causes the -EINVAL error to be returned regardless of any qgroup
flags being set instead of returning the error only when neither of
the flags BTRFS_QGROUP_STATUS_FLAG_RESCAN nor BTRFS_QGROUP_STATUS_FLAG_ON
are set.

A test case for fstests follows up soon.

Fixes: 9593bf4 ("btrfs: qgroup: show more meaningful qgroup_rescan_init error message")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/qgroup.c

@@ -2786,13 +2786,20 @@ qgroup_rescan_init(struct btrfs_fs_info *fs_info, u64 progress_objectid,
 
 	if (!init_flags) {
 		/* we're resuming qgroup rescan at mount time */
-		if (!(fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_RESCAN))
+		if (!(fs_info->qgroup_flags &
+		      BTRFS_QGROUP_STATUS_FLAG_RESCAN)) {
 			btrfs_warn(fs_info,
 			"qgroup rescan init failed, qgroup is not enabled");
-		else if (!(fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_ON))
+			ret = -EINVAL;
+		} else if (!(fs_info->qgroup_flags &
+			     BTRFS_QGROUP_STATUS_FLAG_ON)) {
 			btrfs_warn(fs_info,
 			"qgroup rescan init failed, qgroup rescan is not queued");
-		return -EINVAL;
+			ret = -EINVAL;
+		}
+
+		if (ret)
+			return ret;
 	}
 
 	mutex_lock(&fs_info->qgroup_rescan_lock);