btrfs: set clear_cache if we use usebackuproot

We're currently setting this when we try to load the roots and we see
that usebackuproot is set.  Instead set this at mount option parsing
time.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -2630,9 +2630,6 @@ static int __cold init_tree_roots(struct btrfs_fs_info *fs_info)
 			 */
 			btrfs_set_super_log_root(sb, 0);
 
-			/* We can't trust the free space cache either */
-			btrfs_set_opt(fs_info->mount_opt, CLEAR_CACHE);
-
 			btrfs_warn(fs_info, "try to load backup roots slot %d", i);
 			ret = read_backup_root(fs_info, i);
 			backup_index = ret;

fs/btrfs/super.c

@@ -452,6 +452,12 @@ static int btrfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
 			btrfs_warn(NULL,
 		"'recovery' is deprecated, use 'rescue=usebackuproot' instead");
 			btrfs_set_opt(ctx->mount_opt, USEBACKUPROOT);
+
+			/*
+			 * If we're loading the backup roots we can't trust the
+			 * space cache.
+			 */
+			btrfs_set_opt(ctx->mount_opt, CLEAR_CACHE);
 		}
 		break;
 	case Opt_nologreplay:
@@ -550,6 +556,9 @@ static int btrfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
 		btrfs_warn(NULL,
 			   "'usebackuproot' is deprecated, use 'rescue=usebackuproot' instead");
 		btrfs_set_opt(ctx->mount_opt, USEBACKUPROOT);
+
+		/* If we're loading the backup roots we can't trust the space cache. */
+		btrfs_set_opt(ctx->mount_opt, CLEAR_CACHE);
 		break;
 	case Opt_skip_balance:
 		btrfs_set_opt(ctx->mount_opt, SKIP_BALANCE);