Btrfs: move the R/O check out of btrfs_clean_one_deleted_snapshot()

If the fs is remounted to be R/O, it is unnecessary to call
btrfs_clean_one_deleted_snapshot(), so move the R/O check out of
this function. And besides that, it can make the check logic in the
caller more clear.

Cc: David Sterba <dsterba@suse.cz>
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

fs/btrfs/disk-io.c

@@ -1699,6 +1699,15 @@ static int cleaner_kthread(void *arg)
 		if (!mutex_trylock(&root->fs_info->cleaner_mutex))
 			goto sleep;
 
+		/*
+		 * Avoid the problem that we change the status of the fs
+		 * during the above check and trylock.
+		 */
+		if (need_cleaner_sleep(root)) {
+			mutex_unlock(&root->fs_info->cleaner_mutex);
+			goto sleep;
+		}
+
 		btrfs_run_delayed_iputs(root);
 		again = btrfs_clean_one_deleted_snapshot(root);
 		mutex_unlock(&root->fs_info->cleaner_mutex);

fs/btrfs/transaction.c

@@ -1885,11 +1885,6 @@ int btrfs_clean_one_deleted_snapshot(struct btrfs_root *root)
 	int ret;
 	struct btrfs_fs_info *fs_info = root->fs_info;
 
-	if (fs_info->sb->s_flags & MS_RDONLY) {
-		pr_debug("btrfs: cleaner called for RO fs!\n");
-		return 0;
-	}
-
 	spin_lock(&fs_info->trans_lock);
 	if (list_empty(&fs_info->dead_roots)) {
 		spin_unlock(&fs_info->trans_lock);